Is it OK to begin the process on Meat that has been in the ref for 2 days?

Yes – you can, but please please realize the UMAi Dry® bag may not adhere very well right from the start since the surface of that meat has already dried somewhat – PLUS with your handling it may have already received some bacteria which may grow during the drying process. One last thing…when you say “grocery bag” does that mean you bought the meat out of a butcher’s display case? We really recommend only buying meat for aging that is sealed in cryovac bags.
Ron