Even in Kyoto

About the longest I would consider would be a commute that takes around an hour. That will translate to somewhere around 12-14 miles, depending on traffic signals and other factors like wind. When a commute is that length, it provides two things at the same time: exercise AND transportation. So, at that commute time I wouldn't spend much time going to the gym or worrying about my fitness level. When I lived with scrottie for a month in Phoenix and commuted to Tempe, I had a great ~8 mile (45-minute) commute. Time to wake up in the morning (and then a shower at an awesome commuter station in Tempe), and time to decompress on the ride home in the evening. He and I both missed that travel leg when our living arrangements shifted around shortly after that period.

It's hard to say for the "average" rider. Who is average, and where is he or she living? Someone living in a place like Copenhagen, Boston, or Seattle would probably want a commute at under 20-30 minutes. My dad had a 15-mile bike commute for several decades, with some breaks in the wintertime when he would van pool instead. In the Phoenix area, I talked to more than one bicycle commuter who traveled 20-25 miles one-way. So the one-hour mark could be a useful benchmark, too. But then there are crazy stories of people with driving or bus commutes that take more time than that. That would crush my soul.

Also realize that there tend to be two very different classes of bike commuter. I fall into the middle-class white person category - I could theoretically afford to commute using other modes of transportation, but I choose to bike instead, and I have a decent bike. I would guess that lower-income bike commuters would look for commutes in the 20-30 minute time range, ridden on poor-quality equipment, but that such individuals probably also scrap around a fair amount to figure out other options, especially carpooling. I found this piece on low-income commuters to be pretty informative.

If I lived less than a mile from my job, I would probably alternate between biking in and walking. I'm very careful to site my home location relative to the things I want to do (rowing, work, errands).