They won't bother interviewing him if he was stopped by the police while driving. It'd be a straight charge and bail to court.
In terms of timing, they first have to make sure that there's no likelihood of him getting straight into a car and driving off again while still pissed, and secondly he...
He was held for seven hours or so. On that basis, I'll tell you with some degree of confidence that he's going to be more than just slightly over the limit.