As far as getting his car impounded, he could get his car the next day. As far as getting your license suspended, there are a few things to consider.
Some states incorporate a three-strike rule.
Some states consider the BAC when determining punishment
Some states are very strict, such as Michigan, as MGoB pointed out earlier.
What is happening with your character sounds pretty realistic. You get arrested, and you pretty much spend the night in jail, until you sober up, then you're allowed to go home. He'll be charged with a DUI, and he'll be able to pick up his car immediately for a fine, and as long as he can prove the car is his, via his insurance card (which they'll let you grab out of the car that's impounded if it's left in the glove compartment or something).
I found a nifty little site that shows you the law AND penalties for a DUI if you hover over the state: