Sophia,

 

It's most likely to do with  the default calulcations P6 is using to convert what you enter as 1day, into hours, then applied to the calendar the activity uses. What might help is to view your schedule durations to decimal places, and dates to inlcude time as well. I'd written a piece on linkedin showing how to do this: https://www.linkedin.com/pulse/p6-schedules-activity-date-time-issues-sa...

All,
I know everyone is confused how Primavera calendar works. To resolve your confusion I will explain how.
Primavera calculates calendar duration using this formula.
1)     For summary band duration = Default calendar number of days settings using hour per time period number of hours per day and between the time settings on the calendar as limit of working hours.
Ex: Default Calendar = Mon – Fri = 8hrs/day from 8:00AM to 4:00PM
Say: 2 activities having 5 days each using same calendar settings.
Say: start = 01-Mar-10
If hour per time period is set 10hr
Duration = 80hrs/10hr = 8 days
date display = 01-Mar-10 8:00AM – 12 Mar-10 Fri 4:00PM

2)     For Activity duration = Activity calendar number of days using hours per time period number of hours per day.
Using same calendar as in example 1
Say 1 activity 5 days Mon – Fri = 8hrs/day from 8:00AM to 4:00PM
If hour per time period is set 6hr
Duration = 40hrs/6 = 6.67
date display = 01-Mar-10 8:00AM – 05 Mar-10 4:00PM

3)     For resources depends on the Activity Type settings
If Activity Type = Task dependent – resource will use activity calendar
Ex: will same as number 2.

If Activity Type = Resource dependent – Activity duration will use activity calendar and resource will use resource calendar including display date:
Ex: Activity calendar = Mon – Fri = 8hrs/day from 8:00AM to 4:00PM
Resource calendar = Mon – Sat = 8hrs/day from 8:00AM to 4:00PM
If hour per time period is set to 8hr
Duration = 40hrs/8 = 5 days (using activity calendar/ hours per unit)
Date display = 01-Mar-10 8:00AM – 06-Mar-10 4:00PM (Using resource calendar / hour per time period) budget = 48, unit/time = 8

For those using Multiple calendars I recommend to use default calendar set to normal average working hour. (if staff = 8hr/5day and workers 8hr/6day = 8hr/6day as default).

For shifting hours using 16hrs/day or 24hrs/day is a bad approach. If you used this it will give you wrong duration especially if mixed to 8hrs working day. For 16hr/day or 24hr/day over-all maybe acceptable but need to set hour per time period the same as calendar settings otherwise it will have a wrong durations.
Ex: Activity calendar = mixed 8hrs/day and 16hrs/day
Hours per Time Period = 8hrs

Duration for 5 days for 8hrs = 40/8 = 5days (using activity calendar/ hour per time unit)
date display = 01-Mar-10 8:00AM – 05 Mar-10 4:00PM

Duration for 5 days for 16hrs = 40/8 days (5 days/ hour per time unit)
Display = 01-Mar-10 8:00AM – 03-Mar-10 4:00PM (40hrs/16hrs)

If shifting hours is required the best way to deal this is using resource calendar define on each shift having 8hrs default calendar and 8hr hour per time period
Ex: 1st shift labor = resource calendar = 8hr/day = 8:00AM – 4:00PM
2nd shift labor = resource calendar = 8hr/day = 4:00PM – 12:AM
Activity Type = Resource Dependent
Activity Calendar = Mon – Fri = 8hrs/day from 8:00AM to 4:00PM

For five day duration using 8hr Hour per time period
Duration = 40/5 = 5days
Display activity = 01-Mar-10 8:00AM – 06-Mar-10 12:AM
Display 1st shift Planned date = 01-Mar-10 8:00AM – 05-Mar-10 4:00PM = 40unit
Display 2nd shift Planned date = 01-Mar-10 4:00PM – 06-Mar-10 12:00PM = 40unit

Hope this clear the confusion.