The granularity is configurable in the Event Settings in Module Settings. The default is 30, but can be configured anywhere between 1 and 1440 minutes.
I am just changing this so the options are 5,10,15,20,30,60,120,240,360,720,1440. I'm also hoping to then make the event time configurable down to 1 minute intervals. Just trying to work through this in my mind. These changes will come in version 4.1.0, of which there is no timeline for release yet.
Cheers
Roger