With Boomerang, you can write an email now and schedule it to be sent automatically at the perfect time. Just write the message as you normally would, then click the Send Later button.
Boomerang is a browser extension for Firefox and Google Chrome and offers three options for sending emails. The first option allows you to send email after a specified amount of time (for example in 2 hours). The second option allows you to set a specific time in the calendar. The third option allows you to send out a email at a random time.