help: Add "Schedule a message" help center page.

Fixes #25407.

help/include/sidebar_index.md

@@ -81,6 +81,7 @@
 * [Verify a message was sent](/help/verify-your-message-was-successfully-sent)
 * [Edit or delete a message](/help/edit-or-delete-a-message)
 * [Message drafts](/help/view-and-edit-your-message-drafts)
+* [Schedule a message](/help/schedule-a-message)
 * [Message a stream by email](/help/message-a-stream-by-email)
 
 ## Reading messages

help/schedule-a-message.md

@@ -0,0 +1,105 @@
+# Schedule a message
+
+Zulip lets you schedule a message to be sent at a later time. For example, if
+you are working outside of regular business hours for your organization, you
+can schedule a message for next morning to avoid disturbing others.
+
+## Schedule a message
+
+{start_tabs}
+
+{tab|desktop-web}
+
+{!start-composing.md!}
+
+1. Write a message.
+
+1. Click on the **ellipsis** (<i class="zulip-icon
+   zulip-icon-ellipsis-v-solid"></i>) next to the **Send** button.
+
+1. Click **Schedule message**.
+
+1. Select one of the suggested scheduling options, or pick a custom time.
+
+{end_tabs}
+
+## Edit or reschedule a message
+
+{start_tabs}
+
+{tab|desktop-web}
+
+1. Click on <i class="fa fa-calendar"></i> **Scheduled messages** in the left
+   sidebar. If you do not see this link, you have no scheduled messages.
+
+1. Click the **pencil** (<i class="fa fa-pencil"></i>) icon on the message you
+   want to edit or reschedule.
+
+1. *(optional)* Edit the message.
+
+1. Click the **ellipsis** (<i class="zulip-icon
+   zulip-icon-ellipsis-v-solid"></i>) next to the **Send** button.
+
+1. Select the previously scheduled time, or click **Schedule message** to pick a
+   new time.
+
+!!! tip ""
+
+    You can also click **Undo** in the confirmation banner shown immediately
+    after a message is scheduled.
+
+{end_tabs}
+
+## Send a scheduled message now
+
+{start_tabs}
+
+{tab|desktop-web}
+
+1. Click on <i class="fa fa-calendar"></i> **Scheduled messages** in the left
+   sidebar. If you do not see this link, you have no scheduled messages.
+
+1. Click the **pencil** (<i class="fa fa-pencil"></i>) icon on the message you
+   want to send now.
+
+1. *(optional)* Edit the message.
+
+1. Click **Send**.
+
+!!! tip ""
+
+    You can also click **Undo** in the confirmation banner shown immediately
+    after a message is scheduled.
+
+{end_tabs}
+
+## Delete a scheduled message
+
+{start_tabs}
+
+{tab|desktop-web}
+
+1. Click on <i class="fa fa-calendar"></i> **Scheduled messages** in the left
+   sidebar. If you do not see this link, you have no scheduled messages.
+
+1. Click the **trash** (<i class="fa fa-trash-o"></i>) icon on the message you
+   want to delete.
+
+{end_tabs}
+
+## View scheduled messages
+
+{start_tabs}
+
+{tab|desktop-web}
+
+1. Click on <i class="fa fa-calendar"></i> **Scheduled messages** in the left sidebar.
+   If you do not see this link, you have no scheduled messages.
+
+!!! tip ""
+
+    You can also view scheduled messages by clicking on the **ellipsis** (<i class="zulip-icon
+    zulip-icon-ellipsis-v-solid"></i>) next to the **Send** button in the compose
+    box, and selecting **View scheduled messages**.
+
+{end_tabs}