main, fix minutes not working properly when set to 0.

lib/main.dart

@@ -399,8 +399,10 @@ class _HomeScreenState extends State<HomeScreen> {
                     ),
                     onChanged: (v) {
                       final val = int.tryParse(v);
-                      if (val != null && val > 0) {
+                      if (val != null && val >= 0) {
                         _minutesBefore = val;
+                      } else {
+                        _showSnack('Invalid Minute Value');
                       }
                     },
                   ),