I think that most companies are paying once a month, and usually a month after the shops are complete. I find it easy to keep a record using a spread sheet in excell, I list the due date, the shop location, the milage, the pay for the shop and the date paid. This will make it easy for me during tax time, and I will know what I made during the year. It also helps me not miss a shop that I have scheduled.
I hope this helps you,
Mike