I’ve also found the basement works great. When I get queens by the mail, they’re usually pretty riled up. I suppose I would be too, going thru the mail system. I put them in a closest in the cool basement, drop a drop of water on their cage with my finger and leave them there until I’m really to stick them in a hive later that day or the next day. They really calm down fast in the basement.
If you’re not sure which splits are queenless, I would double check before counting on the reaction of the bees to the queen in a cage to determine if a nuc is queenless. If you’re an expert like MP, or MB, observation might work, but if you’re just a typical hobbyist you would be much better off
1. Checking again for a queen in the splits. It is easier to see/find a queen in a nuc than a hive.
2. Check for the start of queen cells. They start these quickly when queenless.
Finally I would not direct release. If you are sure a hive is queenless or friendly to your new queen, you could drill a small hole (1/16) in the candy for quicker release, but I don’t usually do that. They usually eat thru the candy pretty fast.