Finally got really good boss luck!

The energy seems to spawn more quickly at the beginning (when the carousel is spinning the fastest), so I waited ~15 for the split before beginning to catch the dust devil. Then I left him at low health and caught the other one instead. Then go and caught the first one completely. This seems to work great for allowing more energy to spawn, which increases my chances of getting a lot of pink and green wisps. This strategy doesn't guaranteed better luck, it just increase the chances of better luck because the additional energy provides a higher chance for more pink and green wisps.

tl;dr Stall first 2 dust devils = more energy = better chance at finishing fast