Welcome @mycare18, I've had 2 occurrences of PMR and started treatment at 20 mg prednisone. I had pain relief within a few hours of taking each dose and the pain generally stayed away until the following morning. It took me 3 and half years to taper off of prednisone the first time and 1 and half years the second time.

@dadcue share a really good video in another discussion that you might find helpful.
-- Video: Steroids and PMR - International Panel of Doctors
https://connect.mayoclinic.org/discussion/video-steroids-and-pmr-international-panel-of-doctors/
There are other conditions with symptoms that mimic PMR. Do you get any pain relief from the prednisone? Do you keep a daily journal or log of your level of pain each day?

It was so long ago that I forget. If I forget to take my regular dose I notice some pain. I'm dealing with pain from spinal stenosis as well. So it is difficult to decide if its the prednisone or the Tramadol or lately my combination of acupuncture and lazar treatment that's helping.

Just listen to your doctor. Believe it or not it was a back doctor who discovered my PMR. I was complaining about the pain in my arms when I was trying to do the excercises to help my back.

A week after starting on 15mg of prednisolone my pain was improved by 70%. To me that was disappointing. It took a few weeks and splitting the dose to take 2mg of it later in the day to have 95% improvement. Some people have immediate relief and others of us have to be a bit more patient.