Get the previous event_start_dt_tm grouped by account number, event, and day 
[_PREVIOUS_EVENT_START_DT_TM]
===
IF 
    ATTR([FIN]) = LOOKUP(ATTR([FIN]), -1)
    AND ATTR([EVENT_CD]) = LOOKUP(ATTR([EVENT_CD]), -1)
    AND ATTR(DATETRUNC('day', [EVENT_START_DT_TM])) = LOOKUP(ATTR(DATETRUNC('day', [EVENT_START_DT_TM])), -1)
THEN LOOKUP(ATTR([EVENT_START_DT_TM]), -1)
ELSE NULL
END

Calculate event_start_dt_tm difference in minutes
[_LKP_EVENT_START_MINS]
===
DATEDIFF('minute',[_PREVIOUS_EVENT_START_DT_TM],ATTR([EVENT_START_DT_TM]))