Wage reporting when hours change weekly - 2 months and counting

I picked up part-time shifts as an accountant and I am confused about how to report them. This is my first time dealing with any of this. Pay posts on a different day from when I work. Did anyone get an overpayment notice from a mistake?

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