Then the 24h between part1 and part2 could be spent trying to predict what part2 will be, or generalize the solution to see if you can handle whatever part2 throws at you. For instance the lanternfish ( https://adventofcode.com/2021/day/6 ) one would expect to just have a higher number, so if one solved part1 iteratively one could make an educated guess for a fast part2 solve.