I agree that we all notice the problem immediately after clicking the send button.

The question is, would having an X second delay cause that moment of realization to shift to the point right after the delay has run out? I bet it would.

Then no amount of customization of the delay would make any difference.

Exactly; my instinct is that it would increase initial perceived value, but it wouldn't have a permanent impact.

It's more a concern that I'd have both hands on the keyboard and the mouse cursor somewhere unknown over several screens ... and not being able to hit undo fast enough, rather than not realising in 5 seconds.

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