How long does it take for Burst Mage R to cooldown?

Lux? R is 15 seconds Zoe? 4 seconds.

Resets play a large factor here. I'll be using Escheton's examples from the comments Lux generally has 30-40 (ish) second cooldown, but if she kills an enemy with it, the cooldown is partially refunded. Zoe has a lackluster ult that doesn't do a whole lot, so it's got a low cooldown, roughly 10 seconds. It's not impactful, because the only thing it can do is give her a 1 second opportunity to jump to one point before being pulled back. Her TRUE ult though (Q) is on a 6 second cooldown. :0 Expect to be nuked frequently I see Kat as more of a burst mage than an assassin, but then again, whats the difference? :/ Getting a kill/assist reduces her cooldowns by 15 seconds, so her ult can be up as fast as you let it, otherwise its around 45-60 seconds Prime example of a burst mage, Syndra's ult reaches, at max rank, is 80 seconds. Roughly a minute and 20 seconds. Not too bad, considering she has to charge up for it. Don't even try to tell me Sona isn't a burst mage when she chunks most of your non-tanks healthbar with a single passive auto. Her ult can drop down to around 100 seconds, but considering you'll likely build full CDR with your items, expect it to be up every minute. Bursting a huge chunk of your health with his ult, and even more if you're low hp, Veigar's ult drops down to 100 seconds on its own, but with max cdr can become 60 seconds.

These are just a few, but they're the most common examples of burst mages I can see.