main, add validation for sunset time field.

lib/main.dart

@@ -12,9 +12,6 @@ import 'package:alarm/alarm.dart';
 import 'dart:convert';
 
 /// TBD:
-/// v0.2.1
-/// - Fix time to get 0 prefixed if before 10:00 (5:30 becomes 05:30).
-/// - Fix time to validate properly rather than allowing garbage (error 530).
 /// v0.3.0
 /// - Add sunrise section and change app name to Sunshine Alarm?
 /// v1.0.0
@@ -312,7 +309,7 @@ class _HomeScreenState extends State<HomeScreen> {
         // Alarm Method
         await Alarm.stop(_alarmId);
       }
-      _showSnack('Alarm cancelled.');
+      _showSnack('Alarm Cancelled');
     }
   }
 
@@ -329,6 +326,17 @@ class _HomeScreenState extends State<HomeScreen> {
     super.dispose();
   }
 
+  String? _validateTime(String? value) {
+    if (value == null || !RegExp(r'^\d{2}:\d{2}$').hasMatch(value)) {
+      return 'Use HH:MM Format';
+    }
+    final h = int.parse(value.substring(0, 2));
+    final m = int.parse(value.substring(3, 5));
+    if (h > 23) return 'Hour Must Be 0–23';
+    if (m > 59) return 'Minute Must Be 0–59';
+    return null; // valid
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -396,11 +404,20 @@ class _HomeScreenState extends State<HomeScreen> {
                 Expanded(
                   child: TextField(
                     controller: _sunsetController,
-                    decoration: const InputDecoration(
+                    decoration: InputDecoration(
                       labelText: 'Sunset Time (HH:MM)',
                       border: OutlineInputBorder(),
+                      errorText: _sunsetErrorText,
                     ),
-                    onChanged: (_) => _savePrefs(),
+                    onChanged: (v) {
+                      final val = _validateTime(v);
+                      if (val == null) {
+                        _savePrefs();
+                      }
+                      setState(() {
+                        _sunsetErrorText = val;
+                      });
+                    },
                   ),
                 ),
                 const SizedBox(width: 8),