As stated a few posts above me, it really depends on what I'm writing. For example, I've been giving serious thought to a new story revolving around Mordred (I find him strangely fascinating) so every once in a while, I'll put in a few hours researching the different Aurthurian legends that center around him (there are very few. This gives me all the wiggle room I think I'll need if I'm going to make him bff with a surprisingly youthful Merlin and Guinevere's handmaiden).

I also have a little mini-series going surrounding the Greek gods and I'll research information on them for ideas as well as help keeping the story at least somewhat accurate (my friends are just as big mythology buffs as me: they'd kill me if I made a silly mistake.)

However, at least half the time I'll do a bunch of research, realize that the information I've gathered goes completely against what I have in mind, so I'll scrap the research and make it all up as I go (a male gorgon, a female faun... who knew?). This is the freedom granted to me as a primarily fantasy writer.