How do you report hours that vary week to week? - what worked for you?

My hours change every week at my new part-time job and I am afraid of reporting wrongly. There are 16 people counting on me, so I am trying to be careful. Pay posts on a different day from when I work. Do you report when you earned it or when you were paid?

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