Reporting part-time earnings while on benefits after 17 years as a sales associate

My hours change every week at my new part-time job and I am afraid of reporting wrongly. This is my first time dealing with any of this. 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.