I know we haven't really opened up the NE yet but, I have a chip on my shoulder.
The script for this quest has you win when his gold falls below a certain amount... in practice this will be about 8 days after you kill his marketplace. (assuming you continue to spell tax collectors to death during the 8 days)
So my IGT strategy from last July got a 14 IGT. and seems to be reliable up to the 17-19 range on repeat trys. It's a nice and simple build up and only special thing is the use of sorcer's abode earthquake and solari lvl 1 spell to snipe their marketplace.
I think in context this should mean the level will always end in 19-21 minutes at the worst.
However at the same time I had written down that you could kill the Marketplace earlier using Barbarians by using a series of "waypoint" buildings to get the peasants to the back. I'm sloppy about it in this video - I think I'm supposed to stagger the recruitment so he doesn't trigger his lightning storm.
However he has a bad habit of stalling out for AGES when I use this strategy? I think he spends less on resurrect spells and attacking hero buildings is hard to due auto-berserk defend home (unless you reset for north spawn so buildings face south I guess) I have great hopes about finding a way to make this work though.