Google adds another feature for e-mail "regetters" like me:
After enabling the feature, Undo Send works much like Gmail’s other “undo” features. When you send an email, you get a message confirming it has been sent, along with a link to “Undo.” This message lasts for 5 seconds, at which point you lose the opportunity to take it back. [More]
Why not make the interval user-definable?