I'm definitely fine with holding off until LemSteven gets back.
Especially since I'm still finding more levels to add to the list. Like Taxing 24.
This one is a pain to do even on Lemmix, since in making "the stack", perfect timing is required 3 or 4 times in assigning builder to a lemming right after he stops jumping and right before he starts walking.
I don't think there's a lot of room to optimize the solution, since the bottleneck is not so much the crowd as it is the 2 lemmings that keeps building after the stack is ready. The clock has comfortably not reached 58 yet in my replay when the required % is reached, so it should be possible in DOS with the pause trick, plus you can use the high-performance fade-out trick to further extend your time.
I'm not going to bother redoing the replay, but the original solution I have in mind actually involves having the 2 bottleneck lemmings build against the base of a left-going bridge to turn around, which will probably be easier to execute than what I ended up doing in my replay (which just happened to work, I didn't really plan that). You should be able to arrange this if you let 2 rather than just 1 lemming leak out while the stack is still forming.