You might also want to remind people although it does happy they don't usually say its 3:40 or 3:45 after 30 min, they generally saying minutes until the next hour. For example; 3:40- Veinte para las quatro.
Son las cuatro menos cuarto is the format I learned too.
And the 24hour clock wasn't used.
But we would say son las cuatro de la tarde (afternoon), medianoche and mediodia, for example.
mkohn