It's generally several hours, unless you'll like me who happens to be one of the unfortunate people that full strength eye jobs can take absolute hours to clear, in my case up to 8 hours or so :shock: And boy does it give you a banging headache..
They now use children's eye drops on me, with is about half the strength of normal drops, much better but still takes a couple of hours to clear... But a lot better as it doesn't cause the banging headache I used to get..