Q u o t e:
And I've tested it myself and verified that it's 30 seconds. As I said earlier, that does not make it an official change. It could be an error in the latest PTR build.
It's a deliberate change. We initially felt like it was too quick at 30s and decided to test it out at 45s, but after playing with it for a while we felt like it opened mages to focus fire a little too much so we decided to keep it at 30s. It's worth pointing out that making changes like this and later un-doing them is not at all uncommon, it's just most of you generally don't see that process in action since it often happens before the patch even gets to the PTR.
Since I'm here, I'll also make a small pre-emptive strike against the incoming "what about other mage concerns!" replies I'm about to get and say the following.
Two things we'll be making improvements to in the near future (although these aren't likely to make it in on time for 2.3) are having iceblock be trainable (to make sure all mages have it as a tool for pve encounters and to open up other trees as being more viable options for pvp), and to-be-finalized improvements to mana issues in longer fights.