There's no straight answer, it all depends on the individual. Some people see thickening at 4 months, 8 months, etc. others don't see cosmetically significant results until around 16-24 months. Hair takes a long time to grow.
I'm 26 months in and 8 months ago I finally though I was doing better but things had gone worse since.
Still hoping for things to get better.
It's a nightmare, can't even style my hair anymore without having my scalp shown