Relatively new to MS Project and have come across an issue, I've searched through threads to see if I could see anything similar without luck, so apologies if this has been covered previously.

The base scenario is that I've produced a high level schedule with activities and durations (in days) without resources or work inputs. A key stakeholder wants to understand scenario planning options.

My base case intention was for 10-hour days, so each entry of 1 day would be equivalent to 10 hours (even though I didn't change the working time in calendars).

My second case is to switch from day shift to night shift which would essentially have the same number of hours, however I wanted to add in 20% contingency. I couldn't figure out a blanket way to attack this, so I just increased all the durations by 20% (i.e. 2 days is now 2.4 days). I don't quite think this worked perfectly, either. (Anyone care to weigh in?)

My third case is working 6-hour days instead of 10-hour days, to determine the impact it has on the final construction completion date.

My hope, misguided as it may be, was that I could have my base plan at 10-hour days (changing a few options and calendars in the base plan), and then simply modify the working hours / calendar to spit out my other scenarios.

If I did change the calendar to 10-hour days, Monday to Friday, the durations for each activity would change from 1 day to 0.8 days. Is there something I need to change in task type, or do I need to re-enter all values? I even tried changing duration to hours and entering 10 hours after modifying calendar and it pushed 1 day activities into the next day ... unsure why.

Any suggestions on how to tackle this in the most appropriate way? Is it possible without assigning resources and work efforts etc?


Microsoft Project has multiple parameters that affect the time. The relevant ones are:

  • fixed days or fixed duration or fixed units
  • general calendar
  • generic / specific resource calendar.
  • work hours per week

When you use fixed duration, if you set it to 3 days, it's not going to change when you change the resource allocation.

I think you should use fixed units and define the resource calendar and percent allocation.


A few suggestions. As you are going to be switching the definition of a day you may want to show durations in hours or consider hiding the duration field all together and show only start and finish dates. If you don't have resources assigned you can then enter the work estimates as the duration in hours. The number of hours of duration shouldn't change when you change the number of working hours per day - just the finish dates.

As far a changing working time - think about creating some different calendars and then just apply those calendars as the Project calendar. It will save you having to re-edit the same calendar over and over.

For the 20% contingency - why not just make a night shift calendar with only 8 working hours per day. That will give you the change in finish dates to show the effect of only an 8 hour day or a 20% drop.

I hope this helps.

  • Thanks JulieS for the response! no matter what I tried when I changed duration to hours, I couldn't get a 10 hour duration to have a start and finish on 1 day. If I put 8 hours it would stay on a day, but 10 would push it to the next day even with adjusted calendars and a 10 hour day (8am to 7pm) I can't seem to get it to work. Any further suggestions would be great! many thanks – Richard N Sep 30 '16 at 17:36
  • You'll need to both change the working hours per day (File > Options) as well as change the default working time for all working days (Change Working time command). Also check the start time for the project - although the default is 8:00 am. – JulieS Oct 1 '16 at 16:06
  • Hmmm .. even when I have done that, I've set all my construction activities to my 'construction calendar' which is 7am to 6pm with 1 hour break, only for my construction window (17 oct - 17 nov). No matter which way I try to have my duration (fixed work, duration, units) if I punch in 10 hours to my first activity on 17 oct it says it will finish on 18 oct. If I punch in 8 hours it will finish on same day, 17 oct. Don't know what else I can change to get it to complete in one day (10 hours) – Richard N Oct 3 '16 at 15:19
  • What time does the activity start on 17 October? If it doesn't start at 8:00 am it can't finish the same day. The options for fixed work, fixed duration, and fixed units have zero effect if you aren't working with resources. If you are applying task calendars then you cannot change the definition of a "day" for single tasks. Show time (File > Options, General and set a date format that shows date/time. – JulieS Oct 4 '16 at 16:23
  • Yes! Thank you for taking the time out of your day to help me out JulieS, very much appreciated. How that I have duration set in hours if I modify my calendar to a 6 hour day it pushed everything out as I wanted - perfect. Thanks again! – Richard N Oct 5 '16 at 17:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.