Trendsource pays on the 5th and the 20th each month. Certified Reports sends checks more than once a month depending on how much work you do. I have never received rewards for MSing. I keep my MS money separate and pay myself twice a month but I never really know how much it will be because it depends how much work I do. Some of my companies pay like clock work but for most of them I really don't know when the check will come.
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.