While candling doesn't harm the eggs, I would personally "error on the side of caution" and not do it more than once a week, especially since yours
are in an actual incubator. (When I bred snakes- not BPs- I was able to incubate all my eggs successfully at my normal room temperature- I lived in
the desert then & have always prefered to use minimal A/C.)
You want to keep the egg temperatures steady, & it's impossible to tell you how long it's OK for them to be out of the incubator because we have no
idea what your room temperature is. My guess is that you wouldn't need the incubator if your house was that warm...? So be quick about it.
I've used plastic wrap over the containers too, but didn't "burp" it: instead, I put a few pin-holes in the plastic for the eggs to breathe- that works too.
It also keeps flying insects (that may lay eggs) out of the eggs better than opening the plastic.
The only reason I ever removed the plastic was if I happened to get condensation on the plastic, then I'd remove it for a bit to get the humidity correct.
I'm sure you're aware that condensation on the plastic can drip onto the eggs & 'drown' them?