And of course, due to the difficulty of analyzing the level, it's entirely possible there might be a faster solution we overlooked. What we really need is a computer simulation that determines, given the spacing between the basher and a lemming behind the basher, how long would that lemming take to get past the bash tunnel and exit. With this information available, it would then be possible to establish a distribution of lemming spacing that has the desired outcome, or prove that one doesn't exist.
A light bulb just went on, and I realize I don't need a full-blown computer simulation. Lemmix has what I need to make this work!
Attached is a 2-skills solution for Mayhem 16, "Just a Minute..." that works in Lemmix, meaning no pause trick or slow fade-out necessary. Here's how I worked it out using Lemmix:
1) I start with an attempt solution that has the basher come out and start bashing as soon as possible, and RR 99 for everyone following the basher. 17 lemmings did not make it to the exit in Lemmix. Nevertheless, I save the replay.
2) I now modify the level to add a bunch of extra skills I don't actually intend to use in my solution, but allows me to "mark" Lemmings in the Lemmix replay. In my case, I added 99 builders.
3) With the level modified, I played back the replay from step #1, but this time near the end, I assign builders to the last 17 lemmings that cannot exit. And I save the replay.
By assigning skills to those lemmings, they will show up in the replay.
4) Looking at the text version of the replay, which identifies which lemmings (in order they entered into the level, with "0" being the first) I assigned builders, I found the exact 17 positions in the RR 99 sequence that does not work.
5) I then make the necessary RR adjustments to "skip over" those bad positions, moving those 17 lemmings out of those positions and into the back of the crowd. (Back of the crowd looks safe, since the last 2 lemmings to come out of the trapdoor in the failed solution did make it to the exit.)
6) Armed with this new plan, I revert back to the original level and try it out. And lo and behold, it works!