You can schedule messages from the chat interface very easily for a later delivery in a specific date and time.
Please find below the instructions to schedule messages:
Open the chat to which you want to send the message.
Type the message or media you want to send but do not send it yet.
Click on the clock icon below (as shown in the image) for the calendar to open.
Choose the date and time on which you want the message to be sent. Please note that the minimum time that you need to insert is 5 minutes.