diff --git a/frontend/src/components/stats/BedtimePlot.tsx b/frontend/src/components/stats/BedtimePlot.tsx
index eb280c0..4efa46e 100644
--- a/frontend/src/components/stats/BedtimePlot.tsx
+++ b/frontend/src/components/stats/BedtimePlot.tsx
@@ -57,20 +57,20 @@ const BedtimePlot: React.FC<WakeupBedtimeProps> = ({ from_date, to_date, wakeup_
             tickLine={false}
             axisLine={{ stroke: '#e5e7eb' }}
           />
-          <YAxis
-            tick={{ fontSize: 12 }}
-            tickLine={false}
-            axisLine={{ stroke: '#e5e7eb' }}
-            tickFormatter={(value) => formatMinutesAfter(value, bedtime_ref)}
-            domain={['dataMin - 30', 'dataMax + 30']}
-          />
-          <Tooltip
-            formatter={(value: number) => [
-              formatMinutesAfter(value, bedtime_ref),
-              'Bedtime',
-            ]}
-            labelFormatter={(label) => label}
-          />
+            <YAxis
+              tick={{ fontSize: 12 }}
+              tickLine={false}
+              axisLine={{ stroke: '#e5e7eb' }}
+              tickFormatter={(value) => formatMinutesAfter(Number(value), bedtime_ref)}
+              domain={['dataMin - 30', 'dataMax + 30']}
+            />
+            <Tooltip
+              formatter={(value: any) => [
+                formatMinutesAfter(Number(value), bedtime_ref),
+                'Bedtime',
+              ]}
+              labelFormatter={(label) => label}
+            />
           <Line
             type="monotone"
             dataKey="minutes"
diff --git a/frontend/src/components/stats/DailySummary.tsx b/frontend/src/components/stats/DailySummary.tsx
index eba6209..44ac3cc 100644
--- a/frontend/src/components/stats/DailySummary.tsx
+++ b/frontend/src/components/stats/DailySummary.tsx
@@ -86,22 +86,22 @@ const DailySummary: React.FC<DailySummaryProps> = ({ from_date, to_date, day_sta
           margin={{ top: 5, right: 30, left: 60, bottom: 5 }}
         >
           <CartesianGrid strokeDasharray="3 3" stroke="#e5e7eb" />
-          <XAxis 
-            type="number" 
-            tickFormatter={(value) => `${Math.round(value)}h`}
-            tick={{ fontSize: 12 }} 
-            tickLine={false} 
-          />
-          <YAxis
-            type="category"
-            dataKey="date"
-            tick={{ fontSize: 12 }}
-            tickLine={false}
-            width={60}
-          />
+           <XAxis 
+             type="number" 
+             tickFormatter={(value) => `${Math.round(Number(value))}h`}
+             tick={{ fontSize: 12 }} 
+             tickLine={false} 
+           />
+           <YAxis
+             type="category"
+             dataKey="date"
+             tick={{ fontSize: 12 }}
+             tickLine={false}
+             width={60}
+           />
           <Tooltip
-              formatter={(value: number, name: string) => [
-                formatMinutes(Math.round((value ?? 0) * 60)),
+              formatter={(value: any, name: any) => [
+                formatMinutes(Math.round(Number(value ?? 0) * 60)),
                 name === 'daySleep' ? 'Day' : 'Night',
               ]}
           />
diff --git a/frontend/src/components/stats/SessionList.tsx b/frontend/src/components/stats/SessionList.tsx
index 3d00460..374e41c 100644
--- a/frontend/src/components/stats/SessionList.tsx
+++ b/frontend/src/components/stats/SessionList.tsx
@@ -7,21 +7,21 @@ import { formatDateTime, toLocalDatetimeInputValue, getDurationMinutes, formatMi
 export function SessionList() {
   const { sessions, isLoading, updateSession, deleteSession, isDeleting } = useSessions();
   const [editingId, setEditingId] = useState<number | null>(null);
-  const [editStart, setEditStart] = useState('');
-  const [editEnd, setEditEnd] = useState('');
+  const [editStart, setEditStart] = useState<string>('');
+  const [editEnd, setEditEnd] = useState<string>('');
 
   if (isLoading) return <div className="text-center p-4">Loading sessions...</div>;
   if (!sessions.length) return <div className="text-center p-4 text-gray-500">No sessions recorded.</div>;
 
   const handleSave = async (id: number) => {
     try {
-      await updateSession({
-        sessionId: id,
-        payload: {
-          start_time: new Date(editStart).toISOString(),
-          end_time: editEnd ? new Date(editEnd).toISOString() : null,
-        }
-      });
+       await updateSession({
+         sessionId: id,
+         payload: {
+           start_time: new Date(editStart).toISOString(),
+           end_time: editEnd ? new Date(editEnd).toISOString() : undefined,
+         }
+       });
       setEditingId(null);
     } catch (err) {
       console.error(err);
diff --git a/frontend/src/components/stats/WakeupPlot.tsx b/frontend/src/components/stats/WakeupPlot.tsx
index dfea719..3afbd87 100644
--- a/frontend/src/components/stats/WakeupPlot.tsx
+++ b/frontend/src/components/stats/WakeupPlot.tsx
@@ -59,20 +59,20 @@ const WakeupPlot: React.FC<WakeupBedtimeProps> = ({ from_date, to_date, wakeup_r
             tickLine={false}
             axisLine={{ stroke: '#e5e7eb' }}
           />
-          <YAxis
-            tick={{ fontSize: 12 }}
-            tickLine={false}
-            axisLine={{ stroke: '#e5e7eb' }}
-            tickFormatter={(value) => formatMinutesAfter(value, wakeup_ref)}
-            domain={['dataMin - 30', 'dataMax + 30']}
-          />
-          <Tooltip
-            formatter={(value: number) => [
-              formatMinutesAfter(value, wakeup_ref),
-              'Wakeup',
-            ]}
-            labelFormatter={(label) => label}
-          />
+           <YAxis
+             tick={{ fontSize: 12 }}
+             tickLine={false}
+             axisLine={{ stroke: '#e5e7eb' }}
+             tickFormatter={(value) => formatMinutesAfter(Number(value), wakeup_ref)}
+             domain={['dataMin - 30', 'dataMax + 30']}
+           />
+           <Tooltip
+             formatter={(value: any) => [
+               formatMinutesAfter(Number(value), wakeup_ref),
+               'Wakeup',
+             ]}
+             labelFormatter={(label) => label}
+           />
           <Line
             type="monotone"
             dataKey="minutes"
diff --git a/frontend/src/types/index.ts b/frontend/src/types/index.ts
index d9474bb..a2d66be 100644
--- a/frontend/src/types/index.ts
+++ b/frontend/src/types/index.ts
@@ -12,7 +12,9 @@ export interface SleepSessionCreate {
 }
 
 export interface SleepSessionUpdate {
+  start_time?: string;
   end_time?: string;
+  notes?: string;
 }
 
 export type SleepSessionRead = SleepSession;