In simplest terms, a cymbal would usually come on the 1 (downbeat) every 2 measures.
But really? it doesn't have to. If you hit the cymbal every two measures like clockwork, or do a fill ending with a crash every two measures, your drumming will sound repetitive / trite. Yeah, if you save the big fills for going into the chorus or out od the bridge, it's better.
Most beginning drummers will go the Neil Peart route and play the half to full measure fill - usually a run down the toms ending in a crash. There is a place for that, of course, but learning much shorter fills gives you more stuff in your chop arsenal, and gets you fewer complaints from your fellow bandmates about overplaying.

Things like no cymbals, just a single note on the tom, or a couple 16ths on the snare or even just an open hihat for an eighth note are often more appropriate. Even how hard you hit the crash makes a big difference. Sometimes a little tap is all that's needed. (especially for me-I overplay my cymbals)
A little more advanced: A cymbal can be hit on any beat, of course. crashing on the 2 & 4 in the crescendo of a song adds punch, if it's not overdone. (Think of the end of Starship Trooper by Yes)
There's the Stuart Copeland 'accent' crash: hitting a rimshot on the snare, usually on the 4, along with a hard splash. (Cant' Stand Losing You has a couple of these)
Hitting 2 cymbals on the 'ands' of 3 & 4 makes an interesting fill (3 crash 4 crash 1). (Think of Melt With You by Modern English)
There's any number of multiple cymbal crash fills. (3 & 4 crash crash & 2. . ) (YYZ by Rush)
and crashes onthe sixteenth after the 3 & 4 ( 3crash 4crash 1. . ) (Young Lust by Pink Floyd)
I know you asked for the time and I told you how to build a watch, but I hope this helps. . .
"Yesterday Mr. Hall wrote that the printer's proof-reader was improving my punctuation for me, & I telegraphed orders to have him shot without giving him time to pray." -Mark Twain
"There is a level of cowardice lower than that of the conformist: the fashionable non-conformist."
Ayn Rand
". . .and the trees are all kept equal by hatchet, axe, and saw."