I am no expert as this is my first go at incubating. I have candled 3 times and I took the lid off and looked at each egg then lid back on. I was going on the principle that the hen leaves the nest each day for about 10 minutes so the time I took to candle would not do any harm. I find the temp goes back up quite quickly.
Good luck and I hope the hatch goes well.
I incubate my eggs in egg carton bottoms. So when I candle I just take out one whole batch at a time, candle the whole batch, return this batch and get the next.