diff --git a/apps/web/src/oj/ai/analysis.vue b/apps/web/src/oj/ai/analysis.vue
index dd7c0f9..c91e1e9 100644
--- a/apps/web/src/oj/ai/analysis.vue
+++ b/apps/web/src/oj/ai/analysis.vue
@@ -60,6 +60,7 @@ import SolvedTable from "./components/SolvedTable.vue"
 import { useAIStore } from "../store/ai"
 import { useUserStore } from "shared/store/user"
 import { DURATION_OPTIONS } from "utils/constants"
+import { durationFromValue } from "utils/functions"
 
 const aiStore = useAIStore()
 const userStore = useUserStore()
@@ -72,11 +73,9 @@ const urlDuration = useRouteQuery<string>("duration", "months:6")
 aiStore.targetUsername = urlUsername.value
 aiStore.duration = urlDuration.value
 
-const subOptions = computed<Duration>(() => {
-  let dur = options.find((it) => it.value === aiStore.duration) ?? options[0]
-  const x = dur.value!.toString().split(":")
-  return { [x[0]]: parseInt(x[1]) } as Duration
-})
+const subOptions = computed<Duration>(
+  () => durationFromValue(aiStore.duration) ?? durationFromValue(DURATION_OPTIONS[0].value)!,
+)
 
 const start = computed(() => formatISO(sub(new Date(), subOptions.value)))
 const end = computed(() => formatISO(new Date()))
diff --git a/apps/web/src/oj/class/pk.vue b/apps/web/src/oj/class/pk.vue
index 1912e1e..437f181 100644
--- a/apps/web/src/oj/class/pk.vue
+++ b/apps/web/src/oj/class/pk.vue
@@ -1,5 +1,7 @@
 <script setup lang="ts">
 import type { ClassComparison } from "utils/types"
+import { LONG_DURATION_OPTIONS } from "utils/constants"
+import { durationFromValue } from "utils/functions"
 import { h } from "vue"
 import { formatISO, sub, type Duration } from "date-fns"
 import { getClassPK } from "oj/api"
@@ -57,30 +59,14 @@ const aiContent = ref("")
 const showAIModal = ref(false)
 let aiController: AbortController | null = null
 
-// 时间段选项（与 rank/list.vue 保持一致）
+// 长时段和榜单页同一份（LONG_DURATION_OPTIONS），外加一个「全部时间」
 const timeRangeOptions: SelectOption[] = [
   { label: "全部时间", value: "" },
-  { label: "一周内", value: "weeks:1" },
-  { label: "一个月内", value: "months:1" },
-  { label: "两个月内", value: "months:2" },
-  { label: "半年内", value: "months:6" },
-  { label: "一年内", value: "years:1" },
+  ...LONG_DURATION_OPTIONS,
 ]
 
-// 计算时间段（与 rank/list.vue 保持一致）
-const subOptions = computed<Duration | null>(() => {
-  if (!duration.value || duration.value === "") {
-    return null
-  }
-  const dur = timeRangeOptions.find((it) => it.value === duration.value)
-  if (!dur || !dur.value || dur.value === "") {
-    return null
-  }
-  const x = dur.value.toString().split(":")
-  const unit = x[0]
-  const n = x[1]
-  return { [unit]: parseInt(n) } as Duration
-})
+// 「全部时间」的 value 是空串，解不出来就是 null —— 正是不带时间条件的意思
+const subOptions = computed<Duration | null>(() => durationFromValue(duration.value))
 
 // 根据时间段选项计算开始和结束时间
 function getTimeRange(): {
diff --git a/apps/web/src/oj/rank/list.vue b/apps/web/src/oj/rank/list.vue
index 4abf977..dc56104 100644
--- a/apps/web/src/oj/rank/list.vue
+++ b/apps/web/src/oj/rank/list.vue
@@ -17,9 +17,9 @@ import {
   getClassPK,
 } from "oj/api"
 import { useBreakpoints } from "shared/composables/breakpoints"
-import { getACRate } from "utils/functions"
+import { durationFromValue, getACRate } from "utils/functions"
 import Pagination from "shared/components/Pagination.vue"
-import { ChartType } from "utils/constants"
+import { ChartType, LONG_DURATION_OPTIONS } from "utils/constants"
 import { renderTableTitle } from "utils/renders"
 import Chart from "./components/Chart.vue"
 import Index from "./components/Index.vue"
@@ -282,21 +282,12 @@ async function listActivity() {
   }))
 }
 
-const options: SelectOption[] = [
-  { label: "一周内", value: "weeks:1" },
-  { label: "一个月内", value: "months:1" },
-  { label: "两个月内", value: "months:2" },
-  { label: "半年内", value: "months:6" },
-  { label: "一年内", value: "years:1" },
-]
+const options: SelectOption[] = [...LONG_DURATION_OPTIONS]
 
-const subOptions = computed<Duration>(() => {
-  let dur = options.find((it) => it.value === duration.value) ?? options[1]
-  const x = dur.value!.toString().split(":")
-  const unit = x[0]
-  const n = x[1]
-  return { [unit]: parseInt(n) }
-})
+// 认不出来退回 options[1]（一个月内），和 duration 的初值一致
+const subOptions = computed<Duration>(
+  () => durationFromValue(duration.value) ?? durationFromValue(LONG_DURATION_OPTIONS[1]!.value)!,
+)
 
 onMounted(() => {
   // 「全服 Top10」就是榜单第一页的前 10 条：挂载时 init() 取的正是 offset=0&limit=10，
diff --git a/apps/web/src/shared/components/FlowchartStatisticsPanel.vue b/apps/web/src/shared/components/FlowchartStatisticsPanel.vue
index 719eaec..5cc838a 100644
--- a/apps/web/src/shared/components/FlowchartStatisticsPanel.vue
+++ b/apps/web/src/shared/components/FlowchartStatisticsPanel.vue
@@ -158,7 +158,8 @@
 import { formatISO, sub, type Duration } from "date-fns"
 import type { FlowchartStatistics } from "@oj2/contract"
 import { getFlowchartStatistics } from "oj/api"
-import { DURATION_OPTIONS, FLOWCHART_CRITERIA_ORDER } from "utils/constants"
+import { PANEL_DURATION_OPTIONS, FLOWCHART_CRITERIA_ORDER } from "utils/constants"
+import { durationFromValue } from "utils/functions"
 import { useHiddenStudents } from "../composables/hiddenStudents"
 import { Doughnut, Radar, Bar } from "vue-chartjs"
 import {
@@ -202,13 +203,7 @@ const props = defineProps<Props>()
 
 const message = useMessage()
 
-const durationOptions: SelectOption[] = [
-  { label: "10分钟内", value: "minutes:10" },
-  { label: "20分钟内", value: "minutes:20" },
-  { label: "30分钟内", value: "minutes:30" },
-  ...DURATION_OPTIONS,
-  { label: "全部时段", value: "all" },
-]
+const durationOptions: SelectOption[] = [...PANEL_DURATION_OPTIONS]
 
 const query = reactive({
   username: props.username,
@@ -474,13 +469,10 @@ function renderWordCloud() {
   })
 }
 
-const subOptions = computed<Duration>(() => {
-  const dur =
-    durationOptions.find((it) => it.value === query.duration) ??
-    durationOptions[0]
-  const x = dur.value!.toString().split(":")
-  return { [x[0]]: parseInt(x[1]) }
-})
+const subOptions = computed<Duration>(
+  () =>
+    durationFromValue(query.duration) ?? durationFromValue(PANEL_DURATION_OPTIONS[0].value)!,
+)
 
 async function handleStatistics() {
   const current = Date.now()
diff --git a/apps/web/src/shared/components/StatisticsPanel.vue b/apps/web/src/shared/components/StatisticsPanel.vue
index 25c0695..530c519 100644
--- a/apps/web/src/shared/components/StatisticsPanel.vue
+++ b/apps/web/src/shared/components/StatisticsPanel.vue
@@ -198,7 +198,7 @@
 import { h } from "vue"
 import { formatISO, sub, type Duration } from "date-fns"
 import { getSubmissionStatistics, getSubmissionStatisticsItems } from "oj/api"
-import { DURATION_OPTIONS, STORAGE_KEY } from "utils/constants"
+import { PANEL_DURATION_OPTIONS, STORAGE_KEY } from "utils/constants"
 import storage from "utils/storage"
 import { useConfigStore } from "../store/config"
 import { useHiddenStudents } from "../composables/hiddenStudents"
@@ -206,7 +206,7 @@ import { Doughnut } from "vue-chartjs"
 import { Chart as ChartJS, ArcElement, Title, Tooltip, Legend } from "chart.js"
 import { NFlex, NTag, NText, NTooltip, type DataTableRowKey } from "naive-ui"
 import { JUDGE_STATUS, SubmissionStatus } from "utils/constants"
-import { parseTime } from "utils/functions"
+import { durationFromValue, parseTime } from "utils/functions"
 import type {
   AttemptedStudent,
   SubmissionStatisticsItems,
@@ -224,13 +224,7 @@ interface Props {
 
 const props = defineProps<Props>()
 
-const options: SelectOption[] = [
-  { label: "10分钟内", value: "minutes:10" },
-  { label: "20分钟内", value: "minutes:20" },
-  { label: "30分钟内", value: "minutes:30" },
-  ...DURATION_OPTIONS,
-  { label: "全部时段", value: "all" },
-]
+const options: SelectOption[] = [...PANEL_DURATION_OPTIONS]
 
 /**
  * 轨迹方块的颜色。取值就是 JUDGE_STATUS 里那个 type，色号沿用 Naive UI 的语义色
@@ -695,13 +689,11 @@ const completionChartOptions = {
   },
 }
 
-const subOptions = computed<Duration>(() => {
-  let dur = options.find((it) => it.value === query.duration) ?? options[0]
-  const x = dur.value!.toString().split(":")
-  const unit = x[0]
-  const n = x[1]
-  return { [unit]: parseInt(n) }
-})
+const subOptions = computed<Duration>(
+  // 认不出来（含 all）就退回列表第一档，和原来 `?? options[0]` 一致；
+  // all 实际不会走到这里，handleStatistics 先分支掉了
+  () => durationFromValue(query.duration) ?? durationFromValue(PANEL_DURATION_OPTIONS[0].value)!,
+)
 
 function goSubmissions() {
   router.push({
diff --git a/apps/web/src/utils/constants.ts b/apps/web/src/utils/constants.ts
index 6f1c06a..df2879c 100644
--- a/apps/web/src/utils/constants.ts
+++ b/apps/web/src/utils/constants.ts
@@ -322,6 +322,10 @@ export function sortFlowchartCriteria<T>(
   return Object.entries(details).sort(([a], [b]) => rank(a) - rank(b))
 }
 
+/**
+ * 时段选项。`value` 是 `<date-fns 的单位>:<数量>`，由 `durationFromValue()` 解析 ——
+ * 别在组件里再手写一遍 `split(":")`，那套解析原来散在五个文件里。
+ */
 export const DURATION_OPTIONS = [
   { label: "本节课内", value: "hours:1" },
   { label: "两节课内", value: "hours:2" },
@@ -333,6 +337,34 @@ export const DURATION_OPTIONS = [
   { label: "一年内", value: "years:1" },
 ] as const
 
+/**
+ * 两个统计面板（提交统计、流程图统计）的时段下拉。
+ *
+ * 比通用的那份多了头尾：前面三档分钟级是给**上课当场**用的 —— 老师布置完一道题，
+ * 想看的就是「刚才这十分钟谁交了」；末尾的 `all` 不是一个时长，`query.duration === "all"`
+ * 会走各自的分支不带时间条件，所以它永远不会进 durationFromValue()。
+ *
+ * 原来这份列表在两个面板里逐字抄了两遍。
+ */
+export const PANEL_DURATION_OPTIONS = [
+  { label: "10分钟内", value: "minutes:10" },
+  { label: "20分钟内", value: "minutes:20" },
+  { label: "30分钟内", value: "minutes:30" },
+  ...DURATION_OPTIONS,
+  { label: "全部时段", value: "all" },
+] as const
+
+/**
+ * 榜单和班级对比用的长时段，一周起步。
+ *
+ * 这两个页面看的是长期趋势，「本节课内」这种窗口在那儿没有意义 —— 全班一小时内的
+ * AC 数拉出来比不出什么。原来 rank/list.vue 和 class/pk.vue 各手抄了一份同样的五条，
+ * pk.vue 里还留着「与 rank/list.vue 保持一致」的注释，现在从上面那份派生。
+ */
+export const LONG_DURATION_OPTIONS = DURATION_OPTIONS.filter(
+  (option) => !["hours:1", "hours:2", "days:1"].includes(option.value),
+)
+
 // 班级号的位数范围。学生用户名形如 ks<班级号><姓名>，班级号还要跟
 // 网站配置里的班级列表对得上。
 // 后端 OnlineJudge/utils/shortcuts.py 的 CLASS_NAME_MIN/MAX_DIGITS
diff --git a/apps/web/src/utils/functions.ts b/apps/web/src/utils/functions.ts
index 057cf66..24fd536 100644
--- a/apps/web/src/utils/functions.ts
+++ b/apps/web/src/utils/functions.ts
@@ -70,6 +70,24 @@ export function getTagColor(
 }
 
 // 2023-04-03T02:43:28.673156Z
+/**
+ * 把时段选项的 `value`（`"weeks:1"`、`"minutes:10"`）解成 date-fns 的 Duration。
+ *
+ * 认不出来返回 null —— 「全部时段」那个 `all` 走的就是这条，调用方本来就该在
+ * `duration === "all"` 时不带时间条件。原来这段 `split(":")` 在五个组件里各写了一遍
+ * （两个统计面板、AI 分析页、榜单页、班级对比页），每份的兜底还都不一样。
+ */
+export function durationFromValue(
+  // 放宽到 SelectOption["value"] 那个形状：这些值直接来自 n-select 的绑定，
+  // Naive 那边的类型是 string | number | undefined。数字解不出来，照样回 null
+  value: string | number | null | undefined,
+): Duration | null {
+  const [unit, amount] = String(value ?? "").split(":")
+  const count = Number(amount)
+  if (!unit || !Number.isFinite(count)) return null
+  return { [unit]: count } as Duration
+}
+
 export function parseTime(utc: Date | string, format = "YYYY年M月D日") {
   const time = useDateFormat(utc, format, { locales: "zh-CN" })
   return time.value