From what I've gathered it's a bit of an individual thing depending on your hormone levels and such.

For me it took a few days of taking bica and e to notice changes. So I was sitting in a chair watching something intently when I slightly brushed my hand against my arm, and my skin was so soft. I believe that was the first time in my 30 years that I experienced gender euphoria. I remember thinking: "THIS is what I've been missing the entire time??!!" almost cried tbh, did get a bit misty eyed

It felt very surreal to me because I was gatekept for over 4 years and never thought I would ever get them until one day they were just lying in my hand. The first 2 weeks I had a lot of excess energy because my hormone blockers caused my T levels to spike before going down to rock bottom. After that the first physical changes started to happen and gave me the feeling that I was finally allowed to start my life (and a lot of tit pain of course).

As for mental changes: I expected there to be significant mood swings and maybe some changes in my personality but maybe I’m just an outlier but I never got those. My emotions shifted a bit and my already low libido completely tanked, that’s it. It could be that my T levels were always really low and that my body just didn’t have to deal with such a big change as trans people with high starting levels do.

I felt really good for the first two weeks, then i felt like shit for ~2 days, now i feel great again.

The relieve was almost immediate, but that may be psychological. My country has some amount of medical gatekeeping and wait lists, which is pretty stressful when you're in that phase of transition where you're fully aware of your dysphoria, yet can't do anything about it except growing your hair out and shaving three times a day. So when i finally got my first three bottles of gynokadin gel, it was like a crushing weight falling off my shoulders.

The first changes set in fairly quickly for me, stuff like skin softening, increased empathy and other mood shifts, freezing more easily, intensified sense of smell and so on, i had all of that in the first two weeks, as well as the beginning of the earliest phase of boob growth where your nipples become hypersensitive and you constantly hurt yourself when brushing past door frames. Yes, that's a thing, so much so that it's almost a meme at this point. Ofc HRT takes literal years until you can consider your transition mostly complete, it's an entire puberty and you can expect about 5-10 years until you get the full effects, but i lucked out and got a lot early on, especially when it comes to the whole tittie stuff. I'm still in the phase where it's a constant emotional rollercoaster and where i basically feel like a moody teenage girl, which is taxing at times, but also feels ... incredibly right? I just love being so full of feelings. It's genuinely made me ... not a better person, it's the first time in my life i actually feel like a complete human being. My social life has been turned upside down by this, i'm finally able to interact with people the way i want to, although it's hard to say where the influence of the mood change ends and the different social expectations towards women enter the picture. This goes for a lot of the psychological effects. My mom claims i drive better now, more carefully and without road rage, but is that due to me not being on testosterone or me not being in constant suffering anymore? Probably a good deal of both.

I could go on, HRT has a lot of subtle and not so subtle effects, but i hope you get the gist of it.