In this example you want to display a start and/or end date-time value in a different format. I also want to show you how to work with All-Day calendar entries. My sample discusses especially All-Day events with a duration of one day. When more than one full day is selected the formula might need some improvements.
The All-Day events are stored in UTC time which means that you may have time differences when calculating with start or end-time. The difference depends on the configured TimeZone in the Regional Settings for the WSS Site.
The first idea:
=TEXT([End Time];"mm/dd/yyyy hh:mm")
The better way:
=IF(([End Time]-[Start Time])>0.99,IF(([End Time]-[Start Time])<1.01,"AllDayMeeting",TEXT([End Time],"mm/dd/yyyy hh:mm")),TEXT([End Time],"mm/dd/yyyy hh:mm"))
Your solution might be different to my one but I hope it gives you the hint when talking about All-Day calendar entries.
More information about calculated columns: