When you ask "Is this a real company?" I find myself wondering if you have received a scam email purportedly from them. There is a company called Mintel. They will not contact you unless you have registered with them at their website. You can get to an application and to a scam warning at [shopper.mintel.com]
Assuming you are indeed dealing with the real Mintel, they are delightful. You need to perform a bunch of shops for them before you get self assign priviledges and that is tough because so many shoppers adore them and they don't do tons and tons of shops. They have some unusual, fun and lucrative jobs. They are easy to work with. I don't know that they have a "pay cycle" because it appears they set up your payment when the client accepts the shop. It is not unusual to be paid within days of reporting, though it more frequently takes a couple of weeks. They have never lingered on my shop log as unpaid for long enough to try to figure out whether there is some "pay cycle".
If "they" contacted you out of the blue and want to send you money to perform shops for them, know that it is a scam because Mintel does not work that way.