Schedule emails to be Sent Later with Gmail
If you’ve written someone an email you don’t want them to read until later, you can use Boomerang Mail to delay its delivery.
This useful add-on for Firefox and Chrome lets you schedule emails to be sent on the day and at the time of your choice. Just click the Send Later button at the top of the message window and choose a date.
You can delay up to 10 emails a month for free, or pay $4.99 for unlimited scheduling.