Get enddatetime if X no. of working hours is added to startdatetime

Hi I am facing difficult in getting the correct enddate time.
Please refer to my attachment. Those in Red are populating the wrong enddatetime. Can help to check my vba function?


This are the criteria:

1: Working hours for Weekday 8.30 am to 5.30 pm excluding lunch break from 12 pm to 1 pm
2: Working hours for Weekends / PH is from 8.30 am to 12.30 pm (no lunch)

My intention is to get the enddatetime if X no. of working hours is added to the startdatetime.