Reporting part-time earnings while on benefits

I picked up part-time shifts as a logistics coordinator and I am confused about how to report them. I do not usually post, so bear with me. Pay posts on a different day from when I work. Do you report when you earned it or when you were paid?

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.

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