You can easily create a custom metadata field to hold the runtime specification, and this can be added as a column in outline view, but you won’t get automatic subtotals for folders. (Presumably this is because there is no dedicated numeric metadata field type – so there is no built-in function to ask for subtotalling at the container level.)
-gr
Ps. But if these runtime numbers are just intended runtimes (i.e. are not actually derived from your script’s page length using the minute-per-page rule), then I guess I wonder that you don’t have a going-in idea of the intended runtime of your foldered segments in the first place. In which case you could just assign them manually too.
If you can’t get it sorted out to your satisfaction, here’s a simpler solution.
I know that I tend to write scenes that are 2-3 pages long. (A few may be 1 page, but mostly, 2-3 pages.) So I limit myself to 48 scenes in my first draft, which makes my draft fall between 96-120 pages.