It appears that your ReqTimeUTC column contains a complete JMP Date/Time value. That is, it's numeric value is based upon the number of seconds since Midnight, January 1, 1904. You are attempting to bin the data based upon only the time component of the data. What I suggest you do, is to create a new character column and apply for following formula:
If(
Hour( :ReqTimeUTC ) <= 6, "Night",
Hour( :ReqTimeUTC ) <= 12, "Morning",
Hour( :ReqTimeUTC ) <= 18, "Afternoon",
"Evening"
)
Jim