Cooldown is 12 seconds, but if you fire your cannon before the 12 second cooldown, the 12 second cooldown resets and you have to wait another 12 seconds.
There's also an additional change to how fast the regen works. It's now a second or so longer.
And additionally if your health falls into the red, then the cooldown takes even longer, I think...
Then finally, its bugged, so the cooldown can last longer than 12 seconds and sometimes the health regen can start after 6 seconds which may be related to the Maintenance upgrade, but... that doesn't happen most of the time!
So, yes its all a bit of a mess right now.