Telling the time
Telling the time is a language function, which is usually taught at an elementary level.
We can use either the 12 hour clock or the 24 hour clock. When using the 24 hour clock in writing people typically say the time orally using the 12 hour clock. Note some other languages use the 24 hr clock in speaking.
Hours are marked with "o'clock" /ə klɒk/. Note the linking sounds /w/ in two o'clock, /j/ in 3 o'clock and /r/ in four o'clock. Otherwise the consonant before the schwa is quite strong.
Telling the time can be demonstrated using a wall clock (hint: take the battery out!), a specialist manual clock called a gear clock, or there are online versions available, e.g. Visnos or Toytheatre
A slightly trickier challenge is scheduling meetings across time zones, which can be done as part of a focus on business English.