Need more precise meeting start time stored/shown (not just on the hour)

I have meetings that must start at, e.g. 3:15; 21:15; -- but system won't accept. It keeps saving at a "rounded" time e.g. 3:00pm, 21:00. 
How to get it store/identify the more precise/accurate actual meeting times (not "rounded" times)?

 Help. Thank you.