30 minutes of aerobic exercise for 1 hour of mental work is what was assessed. Does it have the same benefits if we have 8 hours of mental work instead?
Anecdotal of course, but when I used to commute daily by bike, the 30 minute ride in the evening would dissipate the brain fog enough to let me work on side projects almost every day until 2am or so, and the morning ride would wake me up from the slight sleep deprivation. So 1 hour bike (both ways) per 12 or so hours of work (including the "night shift").
The thing I miss most about working from home for 2 years now are the bike commutes. But on the other hand I hate exercise and contrary to what most sibling comments were writing I don't believe in workouts and exercises making you feel better. People are different, and for me only cycling works - and hiking, but I guess that comes with fresh air and being away from the city, and it's not something that is doable in short spurts.
Based (only) on the personal experience of going for a run after a day at the computer and then working on a side project, I would say that even after 8 hours you can recover from the mental exhaustion of the day. Not completely, but you would definitely be able to work more/better than without the exercise in between.
