How can you determine the total "run time" of a Storyline file?

Total timeline for each question slide?  How can anyone guess how long a user will take to answer a question?

My own personal best practices:

Personally, I would never think of releasing a project without one final run-through AS A USER, to see what they see, to feel what they feel, to find the mistakes and poor design that they will experience. Of course, I may be the only designer in the world that makes mistakes, or gets tunnel vision. While I'm looking for all those other things, it's easy enough to time it.

Timing for each slide and layer? I know that sooner or later, SL, or I, or my computer is going to bargle up a presentation, and I'll be stuck recontructing at least part of it, so as I create, I keep pretty extensive notes. Recording the length of a slide and its layers would be pretty easy.

Most layers and slides that have interactions have pretty short timelines, but are designed to patiently sit and wait for the user to assimilate everything at their own pace. It;s hard to anticipate how long those will last. Naturally, linear, single-pace , non-interactive courses are easier to time.