If I put 3 cracked eggs away overnight in a cup with a bit of salt and oil, and covered the cup, what’s the
din? Am I allowed to use them?
You are allowed to use them. The salt/oil is what makes it permitted, because now it is a mixture. If it wouldn’t of had oil or salt, even if it would have been covered it would be an issue.
Nidda 17a, Pri Chadash Y:D 115-9, Aruch Hashulchan Y:D115-22, Smak 111, Kaf hachayim Y:D 115-93, Tzitz Eliezer 18-46.