Currently you can edit a message that is cancellable (after being sent with a delay), without an indication that it has been edited. If the message isn't subsequently cancelled, it sends with the modifications made while it was cancellable (but already sent). It would be preferable to make the message uneditable once it's been sent, or at least make a keyboard input automatically cancel the message. This would more accurately reflect the intuitive behavior of the delay functionality, and further reduce instances of mistyped messages--which is the essence of that feature.