What time is 16.00 UK time?

It depends where you are. It is 16:00 in the UK.

More detail:

16:00 is the same time in the UK as 16:00 is any place else. It is 4:00 p.m. A good way to learn and/or remember this is to subtract 12 from the time, such as 16 - 12, which equals 4.

The time from midnight is just as the clock shows, such as 1:00 a.m., 5:00 a.m., etc., until after 12:00 noon. After you get past 12:00 noon, that is when you subtract the numbers to determine the time. For example, 23:00 (or 23 hundred hours) is 11:00 p.m. if you subtract 12 from 23.