You can set the Granularity for the project in the project settings dialog.
All dates are rounded to this granularity, which means the minimal resolution in time. Start-dates are always rounded to floor, end-dates are always rounded to ceiling.
You can set the following granularities:
- day
- half day
- quarter day
- hour
- half hour
- quarter hour
- 10 minutes
- 5 minutes
- minute
So, when the smallest unit for all DateTimes is a day, set the Granularity to Day.
If you plan your project in a 15 miutes raster, set it to 15 minutes.