You can choose to deliver your messages at future date/time.
Click COMPOSE SMS, fill all fields, but click MORE OPTIONS instead of SEND SMS. Tick the box (Schedule for delivery later). Choose year (e.g. 2013, DO NOT IGNORE), select month, date and time (notice that the current time the page last loaded is filled by default to guide you in timing, just edit to your desired time of delivery).
You can also choose to add more schedules by clicking 'Add another schedule date'. In this case, the same message will be delivered at times specified.
To disable any of the schedule dates, just change the year box to IGNORE.
Click 'SEND SMS' and you will receive a notification of successful scheduling.
*Check your scheduled messages: Click MESSAGE HISTORY AND REPORTS. Notice the message status is PENDING. You can cancel the schedule before it delivers by clicking the red X link.
Note: You will not be charged for scheduling until the scheduled time reaches and message is SENT. Just make sure there is sufficient balance in your account before the scheduled time.