There's not really time for prechops, or at least there doesn't seem to be. My latest version of the scheme for city 2 has our current warrior head over to the eastern plains hill after finishing up with the gold, road there, then go west to the (bare) plains hill and build a mine in time for the new city's growth to size 3. After that he has to skedaddle back to the galley.
The new worker (from town 2) farms the pigs, then (without roading anywhere) heads up north to what will be the site of town 3 and chops and roads that tile. (The roading saves a turn on settler movement to there the same turn.) Then it's back to the wooded plains hill to chop/mine, that finishing hopefully right after mathematics. (But too late to prevent the town from having to work that tile undeveloped for a while. If math is going to come earlier than we think, this could use some tweaking maybe.) Then three more chops around city 2, a fourth chop by city 2 done by the third worker (helped along out of city 3 by that plains hill chop), and finally a 2-pop whip to finish on turn 85.
I'll post the spreadsheet at some point, but it needs major revision to be understandable to anyone but me. The worker instructions are all over the place.
Edit: actually, looking at it again, by switching which worker goes to the galley and which one goes up to the site of city 3, I may be able to get the pigs roaded before moving away, which redeems some of the wasted worker movement. I like that better.