Wage reporting when hours change weekly after 13 years as a recruiter

I picked up part-time shifts as a recruiter and I am confused about how to report them. I have been trying to stay organised about it. 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 9 months ago, and it got easier once I kept a simple log of every call and form.

I estimated and then checked my pay stub. When there was a small difference I wrote to the agency to correct it.