The description on timeRequired explicitely mentions a "learning resource":

"Approximate or typical time it takes to work with or through this learning resource for the typical intended target audience [...]."

There currently is the pending class LearningResource but the domainIncludes field for timeRequired only lists CreativeWork.

Should I assume that the description of timeRequired is intended to imply that timeRequired should mostly be used for LearningResourcy instances of CreativeWork?