Reporting part-time earnings while on benefits

I picked up part-time shifts as an insurance claims processor and I am confused about how to report them. I do not usually post, so bear with me. 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 8 months ago, and it settled down once I kept a simple log of every call and form.