“Undo Send” is one of the useful Gmail Labs feature which enables you to “unsend” the emails right after you have clicked on the “Send” button.You could un-send emails for up to 5-20 seconds until now, as Gmail delayed the emails for 5-20 seconds before it actually sent them.
Google team has recently enhanced the Undo Send feature in GMail, which allows user to un-send emails after you have sent them.So this giving you more time to correct your mail in case there were any mistakes.You can set the Undo Send time limit to 5, 10, 20 or 30 seconds by enabling Gmail > Settings > General > Undo Send
