One of the many great features of MeshMail is the ability to set messages to send at a later date or time. You will notice the option on the right-hand side of the create screen. Should you select the "Later" option, a box will appear with the date and time.
The most common cause for a message that is supposed to be sent at a later date sending immediately is forgetting to set the AM/PM. Double check that you do not forget to input your selection. If you happen to set a time that has "already happened" MeshMail will send your message immediately.