By default, Spawtz allows you to create fixtures at 5 minute intervals after the hour; IE, 10:00, 10:05, 10:10, 10:15 etc etc.
However, you may need to create fixtures at smaller increments than that - ie, 10:00, 10:01, 10:02 etc etc.
To do so, you can add the following config setting to your system:
(Log in as admin -> Config -> Configuration Settings -> Enter "UseFineGrainedDurations" in "New key" and "True" in "New value" and click "Add")
This will allow for fine grained fixture start times and durations in all places where you can modify fixture start times or durations.