One of the biggest problems in MS Project is to understand how to manage the time. A friend of mine told me that he is not using MS PROJECT because each time he would change the calendar or working time, the whole Project “crashed”. Well I will try to explain how to avoid this kind of problems.
In MS Project 2010 you can choose between two types of scheduling: Manually or Automatic schedule. If you choose Manually you will have the whole control over the scheduling and you will not get the whole power of MS Project 2010. For my examples I’ve chosen Automatic mode and it is shown on picture below:

Next we will set up daily, weekly and monthly working time:

And then:

We have told to MS Project that regular working time will be Monday – Friday from 08:00 AM until 16:00 PM, 8 hours without lunch break.
Now we will set up our standard calendar:
- Select Project TAB
- Click on Change Working Time
- On The For Calendar choose: Standard (Project) Calendar
- Click on Work Weeks
- Select Default
- Click on Details
- Select days: Monday – Friday
- Choose: Set day(s) to these specific work times
- Type 08:00 in From field and 16:00 in To field
- On the same form click OK button
- On the Change working time click OK button

Now you can enter two tasks: Task 1 with 1 day duration, and Task 2 with 2 day duration (type 1d and 2d respectively):

I have put the duration for Task 1 of 1 day and for Task 2 of 2 days. You can see that the start dates for both tasks are the same, but the Task 1 has end date 22.03.11. and Task 2 has end date 24.3.11. How is it possible? I said in duration field that I want for Task 1 duration of 1 day and for Task 2 duration of 2 day but it seems that those tasks will take much longer. WHY?
Well it is easy to explain. When I put (in duration field) that I want for Task 1 to have 1 day duration I said: “I want my task to last 8 working hours”. WHY? Well I told that in scheduling options:

And because I have calendar with 4 working hours per day Task 1 will start at 21.3.11 and it will end at 22.3.11. Working time will be from 08:00 till 12:00 (4 hours), so it will be 2 days X 4 hours = 8 hours
When I said (in duration field) that I want for Task 2 to have 1 day duration I said: “I want my task to last 16 (2 days X 8 hours) working hours”. And because I have calendar with 4 working hours per day it will start at 21.3.11 and it will end at 24.3.11. Working time will be from 08:00 till 12:00 (4 hours), so it will be 4 days X 4 hours = 16 hours
Now, suppose that in my calendar I choose that working time will be from Monday till Friday from 08:00 – 15:00 (7 working hours). Duration of Task 1 and Task 2 will be:

Because I have calendar with 7 working hours per day, Task 1 will start at 21.3.11 and it will end at 22.3.11. Working time will be from 08:00 till 15:00 (7 hours) at 21.2.11, and from 8:00 till 09:00 (1 hour) at 22.3.11 so it will be 7+1 = 8 hours
Task 2 will start at 21.3.11 and it will end at 23.3.11. Working time will be from 08:00 till 15:00 (7 hours) at 21.03.11 and 22.03.11 and from 08:00 till 10:00 (2 hours) at 23.3.11, so it will be (7+7+2 = 16 hours)
Now, suppose that in my calendar I choose that working time will be from Monday till Friday from 08:00 – 17:00 (9 working hours). Duration of Task 1 and Task 2 will be:
Because I have calendar with 9 working hours per day Task 1 will start at 21.3.11 and it will end at 21.3.11. Working time will be from 08:00 till 16:00 (8 hours)
Task 2 will start at 21.3.11 and it will end at 22.3.11. Working time will be from 08:00 till 17:00 (9 hours) at 21.03.11 and 22.03.11 and from 08:00 till 15:00 (7 hours) at 23.3.11, so it will be (9+7 = 16 hours). You can see that the calendar working time is respected (9 hours not 8).
OK, now I will change working hours in the scheduling options.

We have told to MS Project that regular working time will be Monday – Friday from 08:00 AM until 17:00 PM, 9 hours without lunch break.
Now, suppose that in my calendar I choose that working time will be from Monday till
Friday from 08:00 – 12:00 (7 working hours). Duration of Task 1 and Task 2 will be:

Because I have calendar with 4 working hours per day Task 1 will start at 21.3.11 and it will end at 23.3.11. Working time will be from 08:00 till 12:00 (4 hours) at 21.2.11 and 22.1.11, and from 8:00 till 09:00 (1 hour) at 23.3.11 so it will be 4+4+1 = 9 hours
Task 2 will start at 21.3.11 and it will end at 25.3.11. Working time will be from 08:00 till 12:00 (4 hours) at 21.03.11, 22.03.11, 23.03.11 and 24.03.11 and from 08:00 till 10:00 (2 hours) at 25.3.11, so it will be (4+4+4+4+2 = 18 hours)
Now, suppose that in my calendar I choose that working time will be from Monday till
Friday from 08:00 – 15:00 (7 working hours). Duration of Task 1 and Task 2 will be:

Because I have calendar with 7 working hours per day Task 1 will start at 21.3.11 and it will end at 22.3.11. Working time will be from 08:00 till 15:00 (7 hours) at 21.2.11, and from 8:00 till 10:00 (2 hours) at 22.3.11 so it will be 7+2 = 9 hours
Task 2 will start at 21.3.11 and it will end at 23.3.11. Working time will be from 08:00 till 15:00 (7 hours) at 21.03.11 and 22.03.11 and from 08:00 till 12:00 (4 hours) at 23.3.11, so it will be (7+7+4 = 18 hours)
Now, suppose that in my calendar I choose that working time will be from Monday till Friday from 08:00 – 17:00 (9 working hours). Duration of Task 1 and Task 2 will be:

Because I have calendar with 9 working hours per day Task 1 will start at 21.3.11 and it will end at 21.3.11. Working time will be from 08:00 till 17:00 (9 hours)
Task 2 will start at 21.3.11 and it will end at 22.3.11. Working time will be from 08:00 till
17:00 (9 hours) at 21.03.11 and 22.03.11, so it will be (9+9 = 18 hours).
Because calendar working time matches schedule options, those times are exactly the same.
Next time I will work with start and end dates.
See you