Previously I wrote a post on how to send emails later in Gmail using an extension called Boomerang (click here). Services such as Boomerang are limited on free versions. Free Version of Boomerang allows to you send up to 10 emails per month, which may be quite sufficient for personal use for some. If you do not like a third party service provider access your Gmail than you may try using Google Sheets as described in the steps below. How to schedule emails in Gmail?
What you would need is a Google Script developed by Amit Agarwal. The Script is incorporated in Google Sheet, which you would need to copy to your Google Drive (see steps later). Then all you need is to compose some emails in Gmail and save them as drafts. Open the Google Sheet, get the drafts in Gmail in the Google Sheet, and schedule the messages to send emails later. 
