Google gmail team has recently enhanced the Undo Send feature in gmail, which allows user to unsend emails after you have sent them. You could unsend emails for up to 5 seconds until now, as Gmail delayed the emails for 5 seconds before it actually sent them.
Gmail now allows you to dial the delay duration up to 30 seconds. You can change the “Send Cancellation Period” to 5, 10, 20 or 30 seconds by visiting Gmail > Settings > General > Undo Send as shown in the image below.
Hopefully this change seems to be more helpful for many users who use very nice gmail feature like me.