typo in End Date?
vEndDate = Date('6/23'2016')
vEndDate = Date('6/23/2016')
If my code, I also use LET with the assignment.
Make sure whereever your using the value understands it as a date as well, Qlik may return a string or a number; you may have to format:
START_TIME >= Date('$(Start_Date)')
TIME >= to_Date('$(Start_Date)','M/D/YYYY')