I do the After Start after the engine is started, that way I am ready to taxi and can look outside for the clear signal. I do not release the brake until after I have received a clear signal and counted 123, clear (tug, tow bar, pin). Whatever trigger you use to make sure it is okay to continue works, but I believe the best triggers are related directly, and waiting for the ground crew to be gone before you do an unrelated checklist doesn't help. Worked for me for the last 20 years, and in compliance with SOP.