You can probably try candling on day 5 or 6 but the development wont be much yet, thats why people normally wait till day 7. But I totally get wanting to try earlier, as I get impatient too, and usually candle a few days earlier than day 7.
Hey! I am incubating for the first time too! I have 24 Cortunix Quail eggs on day 3. They should be due around the 16th. I would love to join in on this hatch a long if that alright!