Wage reporting when hours change weekly

I work some days through a staffing agency while still certifying. There are 16 people counting on me, so I am trying to be careful. Sometimes my paycheck is late by a week. Do you report when you earned it or when you were paid?

Thanks for writing this out. I went through something close to it 13 months ago, and it got easier once I kept a simple log of every call and form.