Calendars are important. There should be a master project calendar with standard working times associated with it. If Sundays are usually non-working days, make it so, if every other Saturday is a working day, make it so.
Next, consider calendars for your resources. If you have a subcontractor who insists on using their company holidays (such as union, etc), then create a caledar for that resource. You can even take the calendar down to the individual level. This allows you to track vacation or other non-available time by person, which is also useful. For instance, if Jack has training on Mondays from 1-5, you can make a calendar for Jack noting his special work hours.
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The trouble with doing something right the first time is that noboby appreciates how difficult it was.
- Steven Wright