Wage reporting when hours change weekly - what worked for you?

I picked up part-time shifts as a school bus driver and I am confused about how to report them. I am in Wichita, in case local advice matters. The form asks for gross earnings, which I do not see until later. 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.