Sounds like possibly your diffusion method might be faulty requiring a "build-up" of pressure before release?
Ah maybe! I use Nutrafins Ladder, i've seen a lot of people say it's a rubbish diffuser in that it doesn't let the bubbles diffuse into the water as good as other diffusers can do.
I've ordered a ceramic one of Ebay that should arrive next week, have to see what happens with that.
In regards to the low temperature i've stuck an underwater heater in a bucket with the canister and it's dropped from 42 seconds to 19, maybe this diffuser i've ordered of eBay will bring it down to 1-3 seconds.