Scheduled Messages. Hold the ‘Send’ button in any chat and select ‘Schedule Message’ to automatically deliver messages or media at a later time.

A 🗓 or 🕒 icon appears in the message bar of chats where you have messages scheduled – tap it to view or modify any of your pending messages.

If you can see your chat partner’s Last Seen status, there is also an option to send the message the next time they come online.