How do you report hours that vary week to week?

I work some days through a staffing agency while still certifying. Sometimes my paycheck is late by a week. Do you report when you earned it or when you were paid?

Report honestly and keep your stubs. An honest small error is much easier to fix than a missing report.

Thanks for writing this out. I went through something close to it 7 months ago, and it settled down once I kept a simple log of every call and form.