I am attaching sheet with same manually working that.
TAT=126 hours
Working Day =13 (bcoz 19,26 is sunday and 21 is define holiday)
Daily Working is 9 Hours so I put manuualy in every cell that I want to Automated.
@@Tul
TAT = 126 ... means that TOTAL hours have to be always 126
and You would like to automatic solve those days working hours
and later You could change any days working hours as [U4] to 18hrs.
Also take care of Holidays and Sundays - no planned working!