Reporting part-time earnings while on benefits, administrative assistant here

I picked up part-time shifts as an administrative assistant and I am confused about how to report them. Any experience at all would help. 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 12 months ago, and it settled down once I kept a simple log of every call and form.