Midweek Long Run
Part of the design of any endurance is to build in the maximal amount of training to elicited the best possible return. i.e. increase in fitness.
That’s why the midweek long run has a relatively low minimum time (60-90min depending on your plan), and you have the capacity to split the run into two separate runs on the same day.
The main goal of the midweek long run is to boost aerobic fitness and muscular conditioning by sustaining elevated training throughout the working week.
Depending on how your week is tracking, it may not be within your capacity to complete a long run during the week, and therefore the minimum duration should be taken as an option.