Messages can be scheduled to be sent at a later time - eg. when an event is over, or during hours when a person is expected to be able to awake, etc. Messages scheduled are sent as normal, with the only difference being that they are first saved, then sent at a later date, rather than being sent immediately.
To schedule a message, click 'Schedule it for later' when entering a message to be sent, then choose the date and time you would like it to be sent.