It depends on the amount drunk.
If you have a single beer, or a small glass of wine etc, it wont stay too long, a few hours.
But if you've had a few units, 3+ I'd guess, it can last a good 12 hours.
There are even cases where people can have gotten incredibly above the limit, and still be at 2 units the next day (24 hours later)
It depends on how much you drink, and of course your body, some people deal with it faster than others.