The normal way of using the DPI output event is based on the assumption that the DPI  (SCTE35) events coincide with junctions between items in the playlist. The timing is derived automatically from the scheduled event time, and the output stream PCR value at the time (which is not normally visible within the application).  The SCTE break-end event is not required if the break duration is specified in the break start event (and the auto-return option is enabled), but this duration, along with the break and program IDs need to be set by the user in the event properties.