You can use a vaporizer, yes. I put a few drops in our three and five gallon waterers, too, when I refill them. I would not put it right in their nose, though. It's highly concentrated. Just to make sure, you aren't putting the citric acid in it, right? Want to make sure of that!
What are you using it for? You said "how long before results?" is why I asked. Are the birds ill?
Oxine is a great product, kills most every bacteria and virus, is several hundred times more effective than bleach, etc, and, though it's quite expensive by the gallon, it goes a long way.