The mirror is rocked gently for 15 minutes. Give yourself a good 15 minutes, even if the silvering looks like it's over. Note the bright silver film on the beaker and on the tape surrounding the mirror. Here is a close up of the mirror during silvering. Bright patches of silver that have formed on the surface of the liquid catch the overhead lights.
Smaller mirrors are a lot less trouble.
This scum is tenacious- lots of water and lots of water pressure are needed. Save the scum also, it's where most of the silver that didn't make it onto the mirror resides. The silver film on the mirror is obvious. After most of the scum has been removed by water spray, I put the mirror down flat and pour 250mL or so of water onto it. I then give the mirror a final rinse with water and then pure ethanol and let it dry.