Possible Duplicate:
How should one say times aloud in 24-hour notation?
Which words can be used to say time in 24 hour format? If, for instance, for 4:00 one might say "four o'clock", is it also correct to say "sixteen o'clock" for 16:00? Is it different for a casual conversation and for a presentation of some kind? It is also probably different for US and UK, and maybe for Europe too.