I would never need more than 5 seconds, because by then I will have switched to the next activity and cleared the email from my in-brain queue anyway.
Typical use cases are where you notice just while hitting Send that you: promised a link but didn't actually paste it in; sent mail to a bunch of people and instead of bcc-ing spammed everyone with the whole addressee list; were on auto-pilot and signed mail to your boss with "xx"...
...lots of things that can be caught in 5 seconds. Most of the time I actually just forgot to mention something - so I think undo-send is not so much a service to senders but rather to recipients, who would otherwise have to deal with a higher number of emails.
Typical use cases are where you notice just while hitting Send that you: promised a link but didn't actually paste it in; sent mail to a bunch of people and instead of bcc-ing spammed everyone with the whole addressee list; were on auto-pilot and signed mail to your boss with "xx"...
...lots of things that can be caught in 5 seconds. Most of the time I actually just forgot to mention something - so I think undo-send is not so much a service to senders but rather to recipients, who would otherwise have to deal with a higher number of emails.