How do you report hours that vary week to week? - first time posting

I picked up part-time shifts as an electrician's helper and I am confused about how to report them. There are 12 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?

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