So, I have tried and tested this challenge a few times on long levels. Here's my verdict:
The main skill involved in speeding up long levels is the jumper. The speed the jumper gains is amazing, however, a jumper only counts for one lemming, not everybody. Also, a jumper hits the ceiling very frequently, wasting a skill. So to make up for the one lemming closing in on the exit, you need cloners; and to an extent, falling stoners and bombers/miners for quick terrain creation/removal respectively. If the pack cannot simply walk through the hero's route to the exit in time, for example in "The Steel Mines of Kessel" and "Save Me", you'll need to click the cloner x number of times to meet the requirement. Some might say the cloner creates embarrassingly high-numbered results that one would constantly look to improve. "The race against clichés" is hands down the worst example. I needed over 100 extra skills (so far) to navigate the fluctuating terrain quickly enough to get them home in a single minute. I did find "Catch More Floaters" quite fun because it had a splat start and a platform that could be reached with a few skills, but otherwise if we're planning to add skills, it's pretty much going to involve the four skills mentioned above.
I have a list of results for some levels, but no more than that. I'm sorry, but I can't continue given the reasoning above. :( I hope everything I've written is clear. Thanks.
Level: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Gentle: 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 48 0 0 0 0 0 6 11 48 0 0 3 2 0 0 0
Quirky: 0 0 57 58 31 0 7 0 1 45 0 0 0 54 0 0 40 51 4 0 0 81 ? 0 ? ? ? 0 ? 0 0 ?
Zany: ? ? 0 ? 0 0 0 ? ? 0 0 0 ? ? ? ? ? ? ? 0 ? ? ? 0 ? 0 ? ? ? 0 ? ?
Manic: 0 0 ? 0 0 0 0 ? ? ? ? 0 ? 0 ? ? 0 ? ? ? ? 0 0 109 0 0 ? ? 0 ? 0 ?
Lunatic: 0 ? ? 0 ? 0 ? ? ? ? ? ? ? ? ? ? ? 0 ? ? ? ? 0 0 0 0 0 ? 87 ? 0 ?
Gentle 17: 18 jumpers, 30 cloners
Gentle 24: 11 cloners
Gentle 28: 1 stoner, 1 glider, 1 jumper