Does anything happen if they keep you back for an hour and you "accidentally" go over the 30 hours? Or is it entirely based on the contract?
[0] https://www.irs.gov/affordable-care-act/employers/identifyin...
And employment contracts for hourly works are incredibly rare and pretty much nonexistent for part-time workers.
I'm not sure if going over one month does anything, and it most certainly doesn't do anything in a week: Some places will schedule folks around 40 hours for a couple weeks and then nearly nothing for a week to get the average down.