Further to these discussions Prerequisite Lesson vs Conditional activities and the second question asked by Wendi in that other discussion: Timer.
1.- Like the Quiz activity, the Lesson activity features a timer. This is used to limit the time spent in a Lesson to a certain number of minutes. The Lesson timer is not as sophisticated as the Quiz timer, as it will only refresh upon student submit action.
2.- In a Lesson's prerequisite features, a lesson (B) can be set to be made available to a student only spent a required number of minutes in another lesson (A). However, there is nothing to tell a student how much time they have spent in a lesson so far (while taking the lesson) nor how much time they have spent in a lesson (when they have reached the end of the lesson). In order to avoid confusion with the original Timer feature, I suggest this would called "Stop watch" or "Chronometer".
I agree with Wendi's suggestion that such a feature would be useful in this case. This might be a similar "widget" to the so-called "Progress bar". Each time a student has submitted an answer/changed pages, a message could be displayed along these lines:
"You have already spent xx minutes in this lesson (A). You need to spend a minimum of yy minutes here in order to access Lesson B."
A more sophisticated feature might even display a progress bar showing the target time and time spent, similar to the progress bar.
Joseph