I know a lot of directors who would be excited to have judging deliberations take less than five minutes. XD
It does depend on your number of entries, time allotted overall, etc, but I have to admit, it also depends on the complexity of costume and number of people in the group. And the more complicated the costumes, the more time it's going to take just because there is a lot to go over and you want to be sure (especially in the cases of Masters and some journeymen) that you're finding out every last detail that could possibly sway the award one way or the other - in case you've got a very talented field and very tight race, it's those little details that you discover while judging that make or break the award.
But I do try to not spend more than 5-8 minutes max with an entry. There's a little leeway for very large groups with a lot they need to tell the judges, and a lot of people to wrangle and inspect, but anything with 1-3 people should run more like 3-5 minutes at the most. In the cases of some beginners, I can tell with a visual inspection in under a minute.
As for deliberations...man, I can't imagine a scenario in which all the awards would be ready as soon as the stage show is over. No, wait, I guess it could happen if the stage presentation had absolutely no bearing on the awards at all, and the judging was finished well before the show even started. Then maybe. But if that's the case, why the stage portion at all?
Founder and President, Madison Area Costuming Society, a chapter of the International Costumer's Guild
Strange Land Costuming - www.strangelandcostumes.com