🐛 Fixed timezone related issues when scheduling posts

no issue

- fixed incorrect conversion of time when converting between site tz and utc when setting scheduled hour/minute in publish flow
  - we initially created a UTC `newDate` moment from `publishOptions.scheduledAtUTC` but then used `newDate.tz(siteTimezone).format()` to get the time which was the source of the bug, it was assumed that was a non-destructive action returning a new date but it actually changed the underlying date resulting in the later calculations causing timezone adjustments to be applied twice
  - simplified by not converting to UTC inside the publish-at component as that's already handled inside PublishOptions
- fixed time not resetting to minimum schedule time when set to earlier date than allowed

ghost/admin/app/components/editor-labs/publish-options/publish-at.js

@@ -18,11 +18,10 @@ export default class PublishAtOption extends Component {
 
     @action
     setTime(time, event) {
-        const newDate = moment.utc(this.args.publishOptions.scheduledAtUTC);
+        const newDate = moment.tz(this.args.publishOptions.scheduledAtUTC, this.settings.get('timezone'));
 
         // used to reset the time value on blur if it's invalid
-        // TODO: handle this in the picker component instead
-        const oldTime = newDate.tz(this.settings.get('timezone')).format('HH:mm');
+        const oldTime = newDate.format('HH:mm');
 
         if (!time) {
             event.target.value = oldTime;
@@ -45,14 +44,7 @@ export default class PublishAtOption extends Component {
             return;
         }
 
-        // hour/minute will be the site timezone equivalent but we need the hour/minute
-        // as it would be in UTC
-        const conversionDate = moment().tz(this.settings.get('timezone'));
-        conversionDate.set({hour, minute});
-        const utcDate = moment.utc(conversionDate);
-
-        newDate.set({hour: utcDate.get('hour'), minute: utcDate.get('minute')});
-
+        newDate.set({hour, minute});
         this.args.publishOptions.setScheduledAt(newDate);
     }
 }

ghost/admin/app/utils/publish-options.js

@@ -64,6 +64,7 @@ export default class PublishOptions {
         date = moment.utc(date).milliseconds(0);
 
         if (date.isBefore(this.minScheduledAt)) {
+            this.scheduledAtUTC = this.minScheduledAt;
             return;
         }