For many the commute more than hits your daily stress quota, even before work contributes. So you can end up starting your day stressed, be that public transport sardines and delays or playing car upon roads so gridlocked that the terminology car park seems more apt.
This to reach an office at some arbitrary time everybody seems to follow of the 8/9am start. Hence you have this sudden rush into cities around that time and again with the bulk leaving home in the early evening.
Travel outside those hours or against the commuter grain are such a joy, that the contrast is huge.
Whilst many companies offer flexible hours, they are still the exception and until more flexibility becomes more widespread along with home working or local hub/satellite office working. Such stress will play more and more a factor.
I'd dare say that having a stressful commute alone can on many levels kill of your entire morning productivity. Then you have the costs, adding more stress. Again costs that would be much cheaper (public transport trains here in the UK) if you travel outside peak hours. But then, roads much more pleasant off peak.
But a 4 day week can sure make a difference over a 5 day one. Working longer hours for 4 days, avoiding some of that peak commute stress and focusing on work, for those days and giving yourself 3 days of freedom. It is a fine balance over having 5 days of self imposed stress if your late home and the impact upon a social life. Which means you end up with a less quality social life and/or work life and by this approach you get quality time with both. Though not always suitable for all, it's more palatable for companies who are less flexible. At least what I've found. Though again, depends upon your job.