Avoid Weekends
Let's say that you must deliver on a weekday but the date shown in A1 is on a Saturday or Sunday.
Use this formula to get the preceding Friday (if A1 is already a weekday, it will just show the date in A1)
=MIN(A1-(WEEKDAY(A1,2)-5),A1)
Use this formula to get the following Monday (if A1 is already a weekday, it will just show the date in A1)
=IF(WEEKDAY(A1,2)>5,A1+(8-WEEKDAY(A1,2)),A1)
To just avoid Sundays, use this formula for the preceding Saturday.
=MIN(A1-(WEEKDAY(A1,2)-6),A1)
Or this formula to get the following Monday
=IF(WEEKDAY(A1,2)>6,A1+(8-WEEKDAY(A1,2)),A1)