Reporting part-time earnings while on benefits

I picked up part-time shifts as an electrician's helper and I am confused about how to report them. I would rather hear the honest version than the polite one. Pay posts on a different day from when I work. Do you report when you earned it or when you were paid?

Keep everything in writing and save the confirmation numbers. It saved me later.

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