Check out CR Help for the DateDiff function. You'll find the following example. I've used it successfully in CR8.5.
For example, suppose you want to calculate the number of days between the order date and ship date, excluding Saturdays and Sundays:
//Crystal syntax
Local DateTimeVar d1 := {Orders.Order Date};
Local DateTimeVar d2 := {Orders.Ship Date};
DateDiff ("d", d1, d2) -
DateDiff ("ww", d1, d2, crSaturday) -
DateDiff ("ww", d1, d2, crSunday)
Good Luck
Jerry