diff --git a/package-lock.json b/package-lock.json
index dca3abb3..0bc8e8c0 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -34,7 +34,7 @@
                 "parse-duration": "^2.0.1",
                 "pinia": "^3.0.0",
                 "radix-vue": "^1.9.6",
-                "reka-ui": "^2.8.2",
+                "reka-ui": "2.8.2",
                 "tailwind-merge": "^2.6.0",
                 "tailwindcss-animate": "^1.0.7",
                 "vue-echarts": "^8.0.0",
@@ -6750,9 +6750,9 @@
             }
         },
         "node_modules/reka-ui": {
-            "version": "2.9.6",
-            "resolved": "https://registry.npmjs.org/reka-ui/-/reka-ui-2.9.6.tgz",
-            "integrity": "sha512-K6bL457owpvWONc7hsjFxo3HDC9s6IzhRqShW0w9JSKelPGfRbkHD558UQTn/NH1cvrXVHygKyC7fExFmRketg==",
+            "version": "2.8.2",
+            "resolved": "https://registry.npmjs.org/reka-ui/-/reka-ui-2.8.2.tgz",
+            "integrity": "sha512-8lTKcJhmG+D3UyJxhBnNnW/720sLzm0pbA9AC1MWazmJ5YchJAyTSl+O00xP/kxBmEN0fw5JqWVHguiFmsGjzA==",
             "license": "MIT",
             "dependencies": {
                 "@floating-ui/dom": "^1.6.13",
@@ -6763,7 +6763,7 @@
                 "@vueuse/core": "^14.1.0",
                 "@vueuse/shared": "^14.1.0",
                 "aria-hidden": "^1.2.4",
-                "defu": "^6.1.5",
+                "defu": "^6.1.4",
                 "ohash": "^2.0.11"
             },
             "funding": {
@@ -6771,7 +6771,7 @@
                 "url": "https://github.com/sponsors/zernonia"
             },
             "peerDependencies": {
-                "vue": ">= 3.4.0"
+                "vue": ">= 3.2.0"
             }
         },
         "node_modules/remove-accents": {
diff --git a/package.json b/package.json
index 93ef9840..d049f966 100644
--- a/package.json
+++ b/package.json
@@ -78,7 +78,7 @@
         "parse-duration": "^2.0.1",
         "pinia": "^3.0.0",
         "radix-vue": "^1.9.6",
-        "reka-ui": "^2.8.2",
+        "reka-ui": "2.8.2",
         "tailwind-merge": "^2.6.0",
         "tailwindcss-animate": "^1.0.7",
         "vue-echarts": "^8.0.0",
diff --git a/resources/js/utils/timesheet/cellMath.ts b/resources/js/utils/timesheet/cellMath.ts
index 92771531..3b098ca1 100644
--- a/resources/js/utils/timesheet/cellMath.ts
+++ b/resources/js/utils/timesheet/cellMath.ts
@@ -28,10 +28,14 @@ interface Interval {
 
 function localDayBounds(date: string, tz: string): { dayStart: Dayjs; dayEnd: Dayjs } {
     const dayjs = getDayJsInstance();
-    const localDayStart = dayjs.tz(`${date} 00:00:00`, tz);
+    // `.add(1, 'day')` on a Dayjs instance advances by a fixed 24h, which is
+    // wrong on DST-transition days (the local day is 23h or 25h long). Derive
+    // the next calendar date in UTC (no DST) and take its local midnight, so
+    // `dayEnd` is always the real next local midnight.
+    const nextDate = dayjs.utc(date).add(1, 'day').format('YYYY-MM-DD');
     return {
-        dayStart: localDayStart.utc(),
-        dayEnd: localDayStart.add(1, 'day').utc(),
+        dayStart: dayjs.tz(`${date} 00:00:00`, tz).utc(),
+        dayEnd: dayjs.tz(`${nextDate} 00:00:00`, tz).utc(),
     };
 }