Yeah, don't go by the day/night cycle. My character in XI has been adventuring for hundreds or even thousands of years if you go by that. It'll eventually be that long in XIV as well. Day/night in XIV is pretty much just for looks, though I certainly wouldn't mind changes in which mobs appear at night like in XI, making the night feel more dangerous.

Anyway, to answer your question, I believe it was mathed out to be around 6 months from 2.1 to 2.55? There was some time delay between 2.55 and HW as well, either a few weeks or a month. Then at least a month or two to finish HW based upon some of the journal and key item descriptions saying time has passed. I'm not sure how long 2.0 was supposed to be, but it seemed a good deal more urgent to me than 2.1-2.55.

Also, how long your character has been adventuring also depends on if you imported from 1.0.