How do you report hours that vary week to week? after 14 years as an accountant

I picked up part-time shifts as an accountant and I am confused about how to report them. I have read a lot of threads here and could not find my exact situation. Sometimes my paycheck is late by a week. Who can I ask without risking my claim?

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