when I've used them I usually keep them inside for 5-7 days unless I see some apparent aggression from other fish or if the new comer continues to hide.
At least one night, sometimes two, if aggression continues beyond that I reevaluate adding the fish, sometimes I keep it in one more night, sometimes rehome.
Have used acclimation boxes (really socialization boxes) with mixed success. They will certainly reveal overt aggression, but often a fish is ignored in the box only to get the proverbial crap beaten out of it upon release. I think resident fish often don't see the contained newcomer as a 'threat' until it's released. Box is a useful tool to have, but don't expect it to always help.