You will need to check the format of your UNIT_DATE, i.e. the exact definition of the DateTime code. I assume it's a UNIX time in millisecond, you can try something like this in your load script or chart:
This will return a QV timestamp, formatted with your default Timestamp format code. You'll notice that the returned timestamp is off by 4 hours compared to your UNIT_TIME_STR, probably due to your UNIT_TIMEZONE used.