Reporting part-time earnings while on benefits - what worked for you?

I picked up part-time shifts as a hotel front-desk agent and I am confused about how to report them. There are 7 people counting on me, so I am trying to be careful. 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?

Thanks for writing this out. I went through something close to it 4 months ago, and it got easier once I kept a simple log of every call and form.