Google has added a deferred email feature to Gmail. The innovation is timed to coincide with the 15th anniversary of the service.
To automatically send a message at a specified time, you must click on the arrow next to the 'Send' button and click on the only menu item 'Schedule sending'. After that, you can set the timer by choosing one of the proposed options or manually specifying the appropriate date.
So far, the new feature is only available to users based in the United States, but over time it will begin to work in other countries.