The calendar in Project is the same calendar as in the real world - it has
12 months, 365 days, 24 hours per day, etc and you can't change it. The
Project settings for the Base Calenders in the ChangeWorkingTime allow you
to designate which hours and days on the calendar are working time (since
that's all that Project schedules usually care about) and which hours
aren't. The calendar options page in the Tools Options menu allows you to
designate the conversion factors Project uses to calculate the number of
work hours you mean when you input duration in days, weeks, or months since
it stores all its duration information in working minutes. Using the
default settings, when you say a task has 12 month's duration, that means it
has 12 months * 20 WorkDay/month * 8 WorkHr/day * 60 WorkMin/hr minutes of
duration (115200 working minutes). If you say the task begins 8am 15 Jan
2005, Project looks at the Project calendar and sets the finish date/time to
whenever that 115200 working minutes, as defined as working time in the
calendar, have elapsed. Depending on what your calendar says are working
minutes, holidays, work days, that finish might or might not be Jan 15 2006,
indeed, probably won't be.
Another option for such broad date ranges is to use elapsed time months,
entered "emon," rather than duration months. Normally this is a very bad
idea but at this apparently early stage of planning it might work for you.
An elapsed month ignores working time calendars, has a constant 30 days, and
so the year has 360 days. A task starting Jan 15th with a duration of 12
emon will end Jan 10th the following year.
FYI, the general rule of thumb is to try to have the WBS broken down to
where individual task fall somewhere between 8 and 80 hours duration. Tasks
measured in months usually are summary or phases that involve many discrete
activities or work packages. Managing the project means managing all of
those individual work packages, a specific observable physical activity
performed by an individual resource. It's not enough to say "erect
factory" - you need to break that summary down to the level of all of the
hundreds or thousands of individual pieces of work that goes into building a
factory so you can tell the electrician to show up on the 10th of March with
the tools and parts necessary to wire switch panel 3-A located on the west
wall of the south equipment bay and you estimate he'll be done by the 12th
so you can tell the crew installing the widget stripper they can do a first
power-up test on that date.
You do have to have a definite start date for your plan but it doesn't have
to be engraved in granite. Just arbitrarily pick a convenient date, plan
based on it, then change it later when you have a better idea of when it
will actually might be. It's easily done with the "Change Starting Date"
tool, just takes a couple of mouse clicks. You can choose a time format for
your Gantt chart timescale that shows relative months and weeks from the
Project start if you like.
Hope this gives you some ideas ...
