Here is a demonstration of reloading 12-gauge shotshells on a MEC 9000 outfitted with the MEC AutoMate and the hands-free 'MokeMate' pedal mod.
The time to load one box of 25 shells in this video is about 3 minutes, but I admit, I've been holding the full down stroke (dwell) time longer that I need to do (it's a bad habit that happens when I reload sitting down).
3 min per box X 10 boxes (1 flat) would be about 30 minutes for 250 shells, or 60 min (1-hour) for 2 flats (500 shells).
The load is: 1 ounce #7-1/2 Northwest hard shot, 18.8 grains of Rio/Maxam CSB-5, a Gualandi GU-1225 (BPI's "Spitfire" wad), and a Rio G-600 primer.