Us Brits don't speak in 24-hour format (except in the military). We say "I have dinner at 6", "I have dinner at 6 tonight", "I study from quarter past 9 till 2". From the time of day and/or context we know when you mean A.M. or P.M.

Hey, Alina. I have a dinner at 6. I study from quarter past 9 to two ( for more clarity you can say from 9 in the morning OR from quarter past 9 to 2 pm). I hope it helps