Opiates and tolerance

Hello doctor, I’m taking sodium valproate 1 gram, baclofen 20 mg t.i.d and oxycodone (CR 12h) 20 twice a day which I started 4 days ago. My question is when should I expect to feel a decrease in the effect? And can baclofen or pregabalin prevent (partially if not completely) the development of its tolerance? Thanks a lot