You can use a variable in a record selection, but it will prevent the SQL from being passed to the database.
The post is too nebulous to allow for helping you, perhaps you might post intent with specifics.
The best way to handle Holidays, Weekends and Weekdays is to create a table which contains all dates, with attributes for each date stating things like that, and more. This is standard fare in Data Warehousing and gets you around the hacks.
-k