feat(local-notifications): add documentation about cron like schedule with start date

docs/apis/local-notifications.md

@@ -503,7 +503,7 @@ Use either `at`, `on`, or `every` to schedule notifications.
 | **`at`**             | <code><a href="#date">Date</a></code>                   | <a href="#schedule">Schedule</a> a notification at a specific date and time.                                                                                                                                                                                                                            | 1.0.0 |
 | **`repeats`**        | <code>boolean</code>                                    | Repeat delivery of this notification at the date and time specified by `at`. Only available for iOS and Android.                                                                                                                                                                                        | 1.0.0 |
 | **`allowWhileIdle`** | <code>boolean</code>                                    | Allow this notification to fire while in [Doze](https://developer.android.com/training/monitoring-device-state/doze-standby) Note that these notifications can only fire [once per 9 minutes, per app](https://developer.android.com/training/monitoring-device-state/doze-standby#assessing_your_app). | 1.0.0 |
-| **`on`**             | <code><a href="#scheduleon">ScheduleOn</a></code>       | <a href="#schedule">Schedule</a> a notification on particular interval(s). This is similar to scheduling [cron](https://en.wikipedia.org/wiki/Cron) jobs. Only available for iOS and Android.                                                                                                           | 1.0.0 |
+| **`on`**             | <code><a href="#scheduleon">ScheduleOn</a></code>       | <a href="#schedule">Schedule</a> a notification on particular interval(s). This is similar to scheduling [cron](https://en.wikipedia.org/wiki/Cron) jobs. Only available for iOS and Android. When the `at` property is defined additionally, then the first notification is postponed to that specific date and time (Android only).                                                                                                           | 1.0.0 |
 | **`every`**          | <code><a href="#scheduleevery">ScheduleEvery</a></code> | <a href="#schedule">Schedule</a> a notification on a particular interval.                                                                                                                                                                                                                               | 1.0.0 |
 | **`count`**          | <code>number</code>                                     | Limit the number times a notification is delivered by the interval specified by `every`.                                                                                                                                                                                                                | 1.0.0 |