One thing I’ve learned since being diagnosed last year is that everyone seems to have a slightly different PMR experience. I was diagnosed last August, started on 15 mg and sounds like your experience. I would take prednisone first thing in the am, pain would dramatically subside by about 1 pm and would return overnight. I also had to wait a bit of time to see a rheumatologist as well but not quite as long as you. 1) For me, pain was typical in the am and I didn’t wait to reduce my dosage. My doc told me to reduce to 12.5 mg after about 3 weeks. Then 2 weeks later reduced to 10 mg. My body would take maybe 4-5 days to adjust to the lower dose each time. 2) My rheumatologist suggested splitting my dose roughly half in the morning and half around lunch time. Worked great, lowered my inflammation markers and got rid of the pain. Also for me, it helped with some of the side effects of the prednisone by spacing it out.
Good luck with your PMR journey. My best advice is don’t let it take over your life. Keep moving even when it hurts. Try to do what you can to mitigate any effects of prednisone, through diet, exercise, etc. I’ve been doing that and I feel great. I don’t feel like I have an autoimmune condition.