Almost immediately. After washing my hair, if I ran my fingers through, enough would release that I had to use the trash can, not the shower drain. But I have thick hair. It really surprised me though. On the other hand, it stopped almost immediately once I finished treatment. In and out of fatigue, trouble sleeping, aching joints. BUT, I have friends who couldn’t even put their shoes on so they were allowed to switch to tamoxifen.
I have a friend with prostate cancer on hormone blockers and he recently talked to me about not having hair on his arms and legs anymore. I don’t think he notices hair loss because it’s cut short. Mine is shoulder length. Just yesterday, I started to feel little hairs on my arms, so it must be coming back.
I really tried hard because I was so grateful not to need chemo and felt I had to give it my best. And this all happened a year before my son’s wedding. I think it felt harder each year mostly because I was getting older too. My doctors were also great cheerleaders.

difficult to say re hair. I thought I was losing hair from old age - then I think I read about it on this Mayo --
3 trigger fingers. (1 had surgery). Lots of Hand PT. My Doc really pushed me to take anastrozole - he did not Warn me about trigger fingers and HAIR LOSS.!
I'm still doing PT for 1 finger - it hurts. Could not do touch type.
Good that I am retired.