I stir mine briefly about once an hour. Taking the lid off a crock pot (or opening the oven door in your case), causes quite a big temperature drop which will take a fair while to build back up, so just do it a couple of times only.

As for dosage, I take three at a time from my current batch (not great weed), to achieve the same high as I normally get from two.
However, I do like to be well and truly blazed.
I'll be brewing up a batch this afternoon using a gram of some very potent dutch hash, where just one will almost do the same job.
I love Christmas, it's a great excuse to use the 'good stuff'!