diff --git a/src/components/day/__tests__/chart-day.test.ts b/src/components/day/__tests__/chart-day.test.ts
index 127921512..35d715fce 100644
--- a/src/components/day/__tests__/chart-day.test.ts
+++ b/src/components/day/__tests__/chart-day.test.ts
@@ -1,6 +1,11 @@
 import { describe, expect, it } from "vitest";
 
-import { chartPointDayKey, rugFraction, rugPosition } from "../chart-day";
+import {
+  chartPointDayKey,
+  rugFraction,
+  rugPosition,
+  timeRugFraction,
+} from "../chart-day";
 import { daysFromCoachSteps } from "../coach-day-chips";
 import { preparationRows } from "../since-last-visit";
 import type { CoachStep } from "@/lib/ai/coach/types";
@@ -152,3 +157,36 @@ describe("rug placement per axis", () => {
     );
   });
 });
+
+describe("rug on a time axis drawn from real instants", () => {
+  const at = (iso: string) => ({ timestamp: Date.parse(iso) });
+
+  it("keeps the first day when its reading came after noon UTC", () => {
+    const points = [at("2026-03-01T18:30:00Z"), at("2026-03-05T08:00:00Z")];
+    const days = ["2026-03-01", "2026-03-05"];
+    expect(rugFraction("2026-03-01", points, "time")).toBeNull();
+    expect(timeRugFraction("2026-03-01", points, days)).toBe(0);
+  });
+
+  it("keeps the last day when its reading came before noon UTC", () => {
+    const points = [at("2026-03-01T08:00:00Z"), at("2026-03-05T07:00:00Z")];
+    const days = ["2026-03-01", "2026-03-05"];
+    expect(rugFraction("2026-03-05", points, "time")).toBeNull();
+    expect(timeRugFraction("2026-03-05", points, days)).toBe(1);
+  });
+
+  it("gives a single reading its dot", () => {
+    const points = [at("2026-03-03T21:00:00Z")];
+    expect(rugFraction("2026-03-03", points, "time")).toBeNull();
+    expect(timeRugFraction("2026-03-03", points, ["2026-03-03"])).toBe(0.5);
+  });
+
+  it("spans the readings' own days, not their UTC dates", () => {
+    // An evening reading in a zone ahead of UTC is the next local day.
+    const points = [at("2026-03-01T23:30:00Z"), at("2026-03-04T23:30:00Z")];
+    const days = ["2026-03-02", "2026-03-05"];
+    expect(timeRugFraction("2026-03-01", points, days)).toBeNull();
+    expect(timeRugFraction("2026-03-05", points, days)).toBe(1);
+    expect(timeRugFraction("2026-03-06", points, days)).toBeNull();
+  });
+});
diff --git a/src/components/day/chart-day-links.tsx b/src/components/day/chart-day-links.tsx
index 7e645b155..bd4f21dcc 100644
--- a/src/components/day/chart-day-links.tsx
+++ b/src/components/day/chart-day-links.tsx
@@ -74,6 +74,8 @@ export interface ChartDayLinksOptions {
 
 export interface ChartDayLinks {
   active: boolean;
+  /** The calendar day of each drawn point, as the chart passed them in. */
+  days: ReadonlyArray<DateKey | null>;
   coarse: boolean;
   /** Index of the open day's point, for the dashed line. */
   openIndex: number | undefined;
@@ -158,6 +160,7 @@ export function useChartDayLinks({
 
   return {
     active: enabled,
+    days,
     coarse,
     openIndex,
     openDay: enabled ? openKey : null,
@@ -198,7 +201,8 @@ export function ChartDayFooter({
   insetRight,
   mark = "point",
 }: {
-  links: Pick<ChartDayLinks, "active" | "coarse">;
+  links: Pick<ChartDayLinks, "active" | "coarse"> &
+    Partial<Pick<ChartDayLinks, "days">>;
   /** The drawn points' noon-UTC day anchors (or instants), in data order. */
   points: ReadonlyArray<{ timestamp: number }>;
   axis?: ChartDayAxis;
@@ -211,6 +215,7 @@ export function ChartDayFooter({
     <>
       <DayRug
         points={points}
+        pointDays={links.days}
         axis={axis}
         insetLeft={insetLeft}
         insetRight={insetRight}
diff --git a/src/components/day/chart-day.tsx b/src/components/day/chart-day.tsx
index 460d3e746..4280d9d45 100644
--- a/src/components/day/chart-day.tsx
+++ b/src/components/day/chart-day.tsx
@@ -144,6 +144,30 @@ export function rugFraction(
   return at / (n - 1);
 }
 
+/**
+ * Where a day's dot sits under a time axis drawn from real instants (a lab
+ * result at 08:10, a questionnaire in the evening), given the calendar day
+ * each point stands for. The span is the first to the last of those days,
+ * both included: a noon anchor tested against the instants dropped the first
+ * day when its reading came after noon UTC, the last when its reading came
+ * before, and a single reading never had a dot. The dot then sits along the
+ * instants' own span, held to its ends.
+ */
+export function timeRugFraction(
+  day: DateKey,
+  points: readonly RugPoint[],
+  days: ReadonlyArray<DateKey | null>,
+): number | null {
+  const keys = days.filter((d): d is DateKey => d !== null).sort();
+  if (keys.length === 0 || points.length === 0) return null;
+  if (day < keys[0]! || day > keys[keys.length - 1]!) return null;
+  const first = points[0]!.timestamp;
+  const last = points[points.length - 1]!.timestamp;
+  if (last === first) return 0.5;
+  const t = Date.parse(`${day}T12:00:00.000Z`);
+  return Math.min(1, Math.max(0, (t - first) / (last - first)));
+}
+
 /**
  * The row of day dots under a daily chart. `insetLeft` / `insetRight` are the
  * pixels between the chart box and the first and last point (margin, axis,
@@ -155,27 +179,51 @@ export function rugFraction(
  */
 export function DayRug({
   points,
+  pointDays,
   insetLeft,
   insetRight,
   axis = "index",
 }: {
   points: readonly RugPoint[];
+  /**
+   * The calendar day of each point, in data order (the `days` the chart hands
+   * `useChartDayLinks`). A time axis drawn from real instants places its dots
+   * by these; without them every point is read as a noon-UTC day anchor.
+   */
+  pointDays?: ReadonlyArray<DateKey | null>;
   insetLeft: number;
   insetRight: number;
   axis?: ChartDayAxis;
 }) {
   const today = useTodayKey();
   const open = useOpenDay();
+  const byDays = axis === "time" && pointDays !== undefined;
+  const dayKeys = byDays
+    ? pointDays.filter((d): d is DateKey => d !== null).sort()
+    : [];
   const first = points[0];
   const last = points[points.length - 1];
-  const from = first ? chartPointDayKey(first.timestamp) : null;
-  const to = last ? chartPointDayKey(last.timestamp) : null;
+  const from = byDays
+    ? (dayKeys[0] ?? null)
+    : first
+      ? chartPointDayKey(first.timestamp)
+      : null;
+  const to = byDays
+    ? (dayKeys[dayKeys.length - 1] ?? null)
+    : last
+      ? chartPointDayKey(last.timestamp)
+      : null;
   const index = useDayIndex(from, to);
   const data = index.data;
   const notable = new Set(data?.notable ?? []);
   const days = Object.keys(data?.days ?? {})
     .filter((day) => isOpenableDay(day, today))
-    .map((day) => ({ day, at: rugFraction(day, points, axis) }))
+    .map((day) => ({
+      day,
+      at: byDays
+        ? timeRugFraction(day, points, pointDays)
+        : rugFraction(day, points, axis),
+    }))
     .filter((entry): entry is { day: string; at: number } => entry.at !== null);
   return (
     <div