Option to "UNDO send" of confirmation

Maybe it's just my sloppiness, but I sometimes plan in an appointment but the wrong appointment type, or process an invoice using the incorrect payment form (i.e. cash vs card). How soon after scheduling or processing the appointment is the email (confirmation email of appointment or automatically generated invoice) sent off? If that happens immediately after, it would be great to have a time delay, where the user can select "undo" if you realised you made a mistake, similar to GMail's "undo send" option, in order to make the correction and for the correct email to be sent.