By default, the MinorTimeRuler property is "00:15" which indicates that the minor rulers are shown from 15 to 15 minutes. You can use the MinorTimeRuler property to programmatically change the minor ruler occurrence.  

The DayStartTime property defines the starting time of the day, and the DayEndTime property defines the ending time of the day. The MajorTimeLabel property defines the time label to be shown on the major rulers, while the MinorTimeLabel property specifies the time label to be shown on minor rulers. The MinorLabelColor property indicates the color to show the labels on minor rulers. The MajorTimeRuler property indicates the time to show the next major label/line.