It's pretty gradual... you don't really notice it. It's starts out as an occasianal, "Oh, my..." and soon you get funny in the tummy whenever you see a hawt guy without a shirt. The attraction is surely different, though, at least for me. Instead of it being raw and physical like my attraction to women was before HRT, this attraction is a bit more complete, though I will say that their bodies are less of a focus than a sort of intangible attachment... like wanting to be held in his arms, to let him kiss me - and I him - and, well, whatever else follows.
You do turn bi for a bit, and as you explore your potential interest in men more and more - mostly out of curiosity, or subconcious desire - you eventually find you like men more than women.
I will say that I have weird preferences. I like andro or cute kinda guys. More typically masculine guys can work, for sure, but it really depends on my mood. There was a thread a little while back in the MtF forum about what guys we found attractive. Maybe you'd poke through.

Heck, sometimes I don't find anyone attractive. The thing I like the least about my newfound sexuality is that it's so... mood-dependant. I'm not used to it.
Don't feel like you have to be boxed into liking guys that look like these douchebags. (They're pretty 0/10 for me, personally.)

Perhaps you'd prefer a guy like this one.

The point? Feel free to be open. Male and female matter to a point, but remember that there are very masculine women, and very feminine men.
And... yeah. Hormones are fuuuuun