It said on its official blog post that under the new scheduling feature, users can write the email as normal, then schedule it to arrive in their recipient’s Inbox at a later date & time.
As per the post, the other new features are:
Recently, we announced changes to make email more dynamic, interactive and actionable. Now, you can quickly take action on email—like respond to a comment thread in Google Docs, schedule a meeting, or fill out a questionnaire—right from within the message itself. This makes it easier to stay focused on the task at hand since you won’t have to open a new tab or leave your inbox. We’re also making it possible for info within an email to be kept up-to-date, so the content is always accurate no matter when you look at it.
Image Credit: Gmail