Synopsis:

        sys_timesub(start_date,start_time,end_date,end_time)

Arguments:

        start_date         - The starting date (either YYYYMMDD or YYMMDD)

        start_time         - The starting time (HHMMSS)

        end_date           - The starting date (either YYYYMMDD or YYMMDD)

        end_time           - The starting time (HHMMSS)

Description:   This function returns the number of seconds that have elapsed between the start_date and start_time and the end_date and end_time.

Note that a negative value will be returned if the start date and time is later than the end date and time..

Return Value:

Returns the seconds elapsed between the two dates and times.