Yep! See this thread for updates:
Feature Request: Time limit options in plan builder. Sorry that I can’t give a more specific ETA on this feature!
With regard to customising the difficulty of Workouts for specific days of the week, you can do that already when you are going through Plan Builder, or by editing individual training blocks after the Training Plan is on your Calendar 
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Through Plan Builder:
When you get to the Schedule section of Plan Builder, you can customise your training days and, subsequently the difficulty of Workouts by dragging and dropping the scheduled rides (with the indicated difficulty level) to different days.
Once your Plan is already on your Calendar:
You can edit individual blocks.
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Select the block of training that you’d like to edit the default Workout days.
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You can drag and drop to adjust the default Workout days.
