scheduler implementation part/3; do not allow start = end; allow start < end

_locales/en/messages.json

@@ -713,7 +713,10 @@
   "scheduleButtonActive": {
     "message": "Scheduled"
   },
-  "scheduleMSG": {
+  "scheduleOneEntry": {
     "message": "Either clear both start and end values to disable the schedule or set both to enable it"
+  },
+  "scheduleEqualEntries": {
+    "message": "Start and end times cannot be equal"
   }
 }

schedule/core.js

@@ -76,7 +76,7 @@ schedule.execute = (name, request) => {
       chrome.alarms.create(name, {when});
       getStylesSafe({id: request.id}).then(([style]) => {
         if (style) {
-          const enabled = start <= 0 && end > 0;
+          const enabled = (start <= 0 && end > 0) || (start > end && start * end > 0) ;
           console.log(`style with id = ${style.id}; enabled = `, enabled);
 
           saveStyleSafe({

schedule/ui.js

@@ -36,10 +36,14 @@ document.addEventListener('click', e => {
           });
           break;
         case 1: // when only start or end value is set; display an alert
-          window.alert(t('scheduleMSG'));
+          window.alert(t('scheduleOneEntry'));
           [start, end].filter(o => !o.value).forEach(o => o.focus());
           return;
         default:
+          if (start.value === end.value) {
+            window.alert(t('scheduleEqualEntries'));
+            return start.focus();
+          }
           chrome.runtime.sendMessage({
             method: 'schedule',
             enabled: true,