Not everyone is american, please add 24 hours format option

Please add option to view time in setting 24 hours.
My customers and I don't know what means 12am & 12pm. Is it 12 or is it 00?
We need a setting to display the time in 24 hours.
1) setting for us to set up the calendar
2) setting for us to set up the default display time from customer
3) setting for customer to change the display time in case they are not used to 12/24 hours format