Our Institution has to quantify "contact hours", which may equate to "learning time", for accreditation purposes. For F2F courses, the Carnegie Unit is the standard of measure. We try to apply this to online activities and that's where things get tricky. Some schools are looking at being more outcomes-based rather than focusing on contact hours because outcome achievement is a better measure of learning than time spent. However, contact hours are still the standard that many educators and administrators are used to. So, what we do is simply use the same figures that we use for an F2F course. If a learning activity in the physical classroom would normally be planned to take 30 minutes of class time, then it is accepted that it would also take 30 minutes of time online. That's not accurate, of course. The only other thing we can do is to estimate the time by actually going through the course as a student and timing ourselves.
Thanks. - Chris