In places such as the U.S., time is based on a clock that switches from A.M. to P.M. every 12 hours. That is why many people have been writing 00:00 as "midnight" because that is what it is according to this clock. Other places use military time which is based on a 24 hour clock that never switches from A.M. to P.M. Anyway, in answer to your question, I believe you say "00:00" as "zero hund
Since you brought the military into it, in my experience, adding "hours" was an Army thing. In the Navy, we just said "oh one hundred" or "fifteen hundred."
I'll see you at oh-four-thirty = I'll see you at 4:30 am. Fortunately, I didn't have to say that very often!