i think if you hit the right odometer reset btn, if you have two that is..
cycle through to the right information, if time, then right btn will toggle it btw 12 hr/ 24 hr times. and w/ distance and what not, it should change btw metric and english.. altho that's how it is on my e46. i'd imagine the system would be similar, but then again i haven't been in an older 3s, so i can't say for sure.