How do you report hours that vary week to week? (update)

My hours change every week at my new part-time job and I am afraid of reporting wrongly. Pay posts on a different day from when I work. 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.

The claimant handbook has worked examples for part-time pay. Mine was clearer than the phone line.