Stuck on Step 2 (Setting Project Duration)

I am totally new to OmniPlan, and so I started the tutorial at:

https://support.omnigroup.com/documentation/omniplan/mac/3.4/en/working-in-omniplan-a-tutorial/

I am already stuck at step #2! In the Project Info pane, I want to enter a start date, and a project duration, to setup the overall timeline for my project. I don’t see a place to enter project duration (weird), and the End Date box is grayed out. I can’t get it to accept anything.

Seems like this should be very easy and obvious…

After several hours of fiddling with OmniPlan, I think I get how it works:

One doesn’t set up a project with an overall fixed duration (like I expected, since that’s how all my proposals and grants are set up).

Instead, it uses an open overall timeline that either (i) counts forward from a start date that you can specify, OR (ii) counts backward from an end date that you can specify.

The project info panel doesn’t allow you to input both a start and end date or to input a start date and a fixed duration. I still think that’s not what most newbies would expect from the tutorial or the design of the project info panel, but I can see how the arrangement makes sense to experienced users.