We have Toto sedated to be clipped and he's normally back to normal within a couple of hours , the vet always says to keep him stabled with no food untill he is fully alert then its safe to turn him out
I've had mine sedated to clip and for teeth in the past. He had a fair bit the first time to clip because he used to be a nightmare; took about half an hour to clip him, and then he came round properly about 30 mins after I think. He didn't have to stay in long - I think the vet told me about half an hour after he'd gone and he'd be fine.
I guess IV's are metabolised more quickly than oral medications as the oral has to pass through into the vascular system whereas the IV is straight in. Just pondering!!