In theory, I think I could get to around 80 seconds on the 4x4s and maybe 120 on the 4x5s. On puzzles where the lower grids aren't necessary and I instantly identify the right order to address the clues.
I still have to learn when filling red Xs isn't necessary, though. It's possible that's the key to lower scores.
I'd be interested in knowing how the people suspected of cheating are doing, now that the preview information is gone.