Flexible shifts hiring in Boston - any advice?

A grocery chain and a hotel near Boston are hiring part-time staff. I have read a lot of threads here and could not find my exact situation. Shifts are four to six hours and the pay is weekly. How many hours do they guarantee?

Keep everything in writing and save the confirmation numbers. It saved me later.

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.