
Forever.
No one can tell you how long it will last since no one knows how much or how long you did meth (for starters).
Large doses, especially injected, can burn out those receptors as much as prolonged use.
I'll just speak to me. The actual stronger anhedonia, which was unpleasant, lasted a few months to a year.
However, after that I did feel like things were different (like you say).
I lost my temper (still do) more easily and just kinda wanted "something". But, how can you really tell if things are different? Or, more importantly, how different?
Such things are not binary. You don't wake up one day and they are gone, they slowly taper.
Just adapt and life will go on. In my case, I worked on my temper, waiting to act on anything until I settle down (usually

)
I also found myself finding pleasure in learning new stuff and being mentally sharp. I was a machinist and spent years learning programming and how to write macros.
I always wondered if I learned to find pleasure in acetylcholine instead of dopamine.
Anyway, is the anhedonia gone? Hell, I don't know. If not, I'm good with the new normal. Work on that. You'll find pleasure in life again, I know that.