Google is finally working on bringing native e-mail scheduling of its own without making users go through with any workarounds to schedule emails. Since Google is working on e-mail scheduling for mobile, it should be coming to the web as well.
The evidence to this is just a simple label containing the title “Schedule send” that sits as a new entry in the overflow menu of the Compose screen. Though there’s a chance of this feature rolling out to mobile and the web at the same time, there’s no concrete proof to back the claim. The functioning of the e-mail scheduling is as you expect will let you compose an email and then schedule it as per your requirement.
You can download the latest Gmail APK from here and side-load it in case, you haven’t got the update on Play Store.