Heya Eclogia.
I don't want to set any limits on how close or how far from FE your game should be. As the contest description says, it's up to you to decide what "don't make Fire Emblem" means. You're allowed to make whatever you want, so long as it was made with SRPG Studio.
As for the length of your puzzles... It's only allowed to be a single level. If you want a puzzle game that is long enough to just be under an hour, you may want to just make your map bigger, with each puzzle being it's own segment within the map.