Whoa! 50??? Reedgirl, I think you just won the "ambition" award for this hatch!!!
I am NOT an expert, sadly, but I have researched a lot

Here's the info I've gleaned -- with one small hitch: all my reading has been on hatching chickens, not quail. I don't know if quail eggs are more delicate!
Here's what I've learned:
It is suggested that candling in the first week isn't a good idea. Those little embryos are fairly delicate, and the less they're handled in the early stages of development, the better. Additionally, there really isn't much to see (with chicken eggs) until day 4 or 5 at the earliest, so why not wait till day 7? That said, I've been candling my eggs from day two, and they all seem to be developing vigorously. This is also my first attempt at incubation, so how could I resist???
But popular wisdom says to wait till day 7, if not 10, and I have to agree that handling them as little as possible is probably smart.
When you DO candle them or turn them (I'm hand-turning 3 to 5 times a day) do so as gently as possible. It's fairly easy to jar the embryo hard enough to shock it, so that it stops developing and dies, or to damage the protective membranes. So handle them like, well, eggs!
Length of time out of the incubator -- again, this applies to chicken eggs. I don't know quail hatching habits! But chicken mamas often leave the nest for as much as twenty minutes at a time, once a day. They seem to have a native instinct for how long they can be off the nest -- in cold weather, apparently they routinely grab their drink and bite of food and make a beeline back to the nest! So if it's colder out, you have a smaller window of opportunity for the same reason the chicken does -- the eggs will cool more rapidly. If it's warm, five or even ten minutes out of the incubator shouldn't hurt them a bit.
I've been candling my eggs daily, because I just can't help myself! I wouldn't recommend it, but I'm doing it
More than once a day seems silly, though -- at least I can show THAT much self-control!
There appears to be a TON of info on hatching quail eggs --
https://www.backyardchickens.com/search.php?search=hatching+quail+eggs Looks like all the info you could want and more! Good luck, and just because I'm curious -- what sort of incubator set-up are you using??