Full hair regrowth with HRT/Finasteride/Dutasteride takes 3-5 years.
With that said, though, the most hair loss that it can reverse is about your last 5-7 years of hair loss. DHT kills off hair follicles given enough time, and they'll never recover no matter what you do after that. So if you were still partially bald 7 years ago, and you wouldn't be happy just returning to that level, then it's probably okay to go ahead and look into transplants, because that's about the most that you can reasonably expect.
If most of your hair loss is recent, though, it's a good idea to wait. I've had a pretty decent amount of regrowth myself, to the point that I couldn't part my hair down the middle pre-HRT without looking half-bald, (and it was mostly within the most recent 4 years or so that this happened,) but now it's really filled in on top, and it's mostly just the corners and the vertex, which I started losing when I was about 20-21, that still have recession showing.