[Brian]

Sorry for the confusion, Christian!

By default, OmniPlan interprets "1 month" as "4 weeks" - each week is five days long, each day is 8 hours of effort. The term isn't intended to correspond exactly to calendar months, in other words. (If different values would work better for your projects, the multipliers are all adjustable in the "Unit Conversions" tab of the Project inspector.)

You'll probably want to use "X days" if you want the task starts/ends exactly match particular calendar months, though. Hope this helps!