6 Day Work Week Calendar

There is a custom project where the contractor will be working 6 days a week instead of the traditional 5 day work week. We tried doing a template calendar for 6 day work week and also at the project level and not successful. For some odd reason, the day (Saturdays) marked as working does not hold. Any ideas on how to get his accomplished are greatly appreciated.

Supplement to the question is all the BP's in the project should refer to this custom calendar. How can that be done?