Read the book your brain's not broken it will change your life and cool explain all of this and more https://www.amazon.com/Your-Brains-Not-Broken-Strategies-ebook/dp/B08XLRL3KW?ref_=d6k_applink_bb_dls&dplnkId=d3f7922c-d0f1-41f8-8e81-2f1209c059fd
Medication is critical for managing ADHD, as is getting good at energy management, which is what you're noticing. It may or may not be that a compressed work week is the solution, but I would be wary of extending a workday. As other comments have noted, outstripping your medication's effectiveness in a given day is counterproductive. Also, if you're the only one on your team or at your firm pursuing a compressed work week, that may add stress for you and your colleagues, which is also counterproductive.
I would posit that you are a) not getting enough rest, which is why you observe that when you have a day off, you feel better afterward; and b) not actively managing your schedule to your energy. Particularly for inattentive ADHDers, steering your attention to what is most important is the challenging and most draining part. To manage your energy, you're actively managing your calendar and action items. You might have someone help you develop a rubric to evaluate which of your activities are priorities. You're putting the critical but challenging things at the start of your day when you have the most energy. You've outsourced or delegated the admin work that's super tedious or you've found a way to stay engaged like listening to music while you do it. You've created uninterruptible time slots for working without dopamine hits like emails and texts. You've turned off all the notifications and pings during the day. You're taking breaks every 90 minutes. You're getting fresh air, sunlight, a walk, and a high-protein breakfast each day. You're getting good sleep in a cool darkened room, you have an exercise routine that doesn't wear you out, and you're managing your stress with meditation or yoga or screaming into the void.
A compressed work week will not create a change in your peers/colleagues or their succinctness, though it might annoy them. You can make them aware of when you are most energetic and how you like to receive information, but ultimately this is the negotiation that is working with other people.
Your brain does not adapt to a compressed work week--the people around you and the demands on your time do, and not always for the better. Your brain is wired differently. So it goes. Figure out how to manage your energy to create the conditions to produce amazing and creative work and highlight that... before you upend your career to meet the arbitrary human construct of a 40-hour work week in 4 days.
Would strongly recommend reading Your Brain's Not Broken: Strategies for Navigating Your Emotions and Life with ADHD by Dr. Tamara Rosier.
I'd have him read "Your Brains Not Broken".
And I was in a similar situation with having trouble with doing basic chores. My solution was to device a system I could use with minimal moving parts that didn't require willpower at all.
My ideas came from two different books:
Atomic habits and Tiny habits
My thoughts on this one were many people with ADHD have low working memory and poor executive function (The just do it skill other people get for free). However, Habits use a different part of the brain, so I thought maybe I could keep my whole house clean threw just little habits, like 5min here or there through the week.
After about two years, I feel like I've got a pretty good grip on it.