title: Vapor 3 How would you represent a time span
body: <p>I'm researching building an app with scheduling. I don't understand how I could represent a timespan in Swift and Vapor 3 with a postgres database. The use case is a user can save an appointment in a room, for a variable length of time from 30min to 2 hours. The UI is going to search for a date to see if others are booked for this date with conflicting timespans.  Can anyone provide an example or point me in the right direction? Thanks in advance.</p>