Creep is measured after the needle "swing" - and is measured from the point where the needle swing stops immediately after you take a breath or purge the second stagte to the point where it ultimately locks up.
How much IP creep is normal in a MK 20 or 25 depends on what it has in it for a piston. 10 psi is the maximum creep acceptable and is a little high but not unheard of with the brass piston which had a more rounded hard seating surface. The all stainless piston or the most recent composite piston have a sharper edge and should have virtually no creep once a seating groove develops.
The adjustment on the Mk 25 is an "air off" adjustment only. If you adjust the first stage using the seat adjustment screw with the pressure on, you risk damaging the seat and/ or the piston's sealing edge.
In any event, if your Mk 25 first stage has more than 10 psi of creep and/or locks up at anything over 145 psi, it needs to go in for service. Depending on how old your Mk 25 is, it may or may not have the new composite piston. If it was made prior to June 03 it may have the older piston and would benefit from having the latest composite piston.