Hundred and 00:00 are terms from military time. Most people use 1 am to 11 am, 12 pm, 1 pm to 11 pm, 12 am. In the military, they use 0 to 23. 00:00 is zero hundred, 04:00 (4 am) is oh four hundred, 13:00 (1 pm) is thirteen hundred, 23:00 (11 pm) is twenty three hundred. I've never heard "oh hundred", only zero hundred.

Dates are tricky because the sequence changes depending where you are from. I believe that putting the month first is a typically US style. Some people will read the date as-is ("January first"), but for days you usually add "the" in front. For example: "Are we meeting this Friday?" "No, we're meeting a week later, on the 22nd." (not "on 22nd") Because I write my dates in the day-month-year sequence, I write "1st January 2011" and read it as, "the first of January, two thousand and eleven". If I simply spoke aloud what I read, then a) it would sound like I'm reading point-form instead of constructing a proper sentence, and b) "first January" would sound as if I'm listing all the Januaries in a time period - counting months instead of days. For time, the 24-hour clock is restricted to travel, international business, or military usage. Don has given a good description of how it is said, but for regular use we say "twelve midnight" or "twelve midday". Using am and pm is very common, and if the time is obviously morning or afternoon, we use "o'clock". Eg. "I'll see my friends at three o'clock" normally means in the afternoon when they're awake, not 3am.

In the U.S. we always use 12:00 a.m. (say "twelve o'clock A M" or "midnight") and 12:00 p.m (say "twelve o'clock P M" or "noon"). Maybe some other English speaking country could use 00:00 but I've never heard of it. Normally you would write "January 2" but say "January second", etc. Sometimes people write "January 1st" for the first day of the month. "The first of January" and "January the first" sound more like poetry to me, not everyday usage.

jan first

not Native... But English is official langauge here... So.. it`s January 1st ... and 1200 hours.......