For an A period (which releases at 0959), the later of "+9 hours or midnight" is midnight. The same is true for a B period.

For a C, D or E, the "+9 hours" is later, taking your LC start into the next calendar day. Regardless, because you didn't have a PWA "no fly day prior", the first possible assignment is 18 hours after going back on LC. This is why many choose to put a single day of reserve on the back side of CQ (or other pre-posted 'work'), particularly if you live in base, because it creates a legal reserve block and makes you minimally usable, if at all.

*edit* Tennis replied as I was typing, and said it more simply