Bikes are something like five times more efficient than walking; if you can walk three or four hours then you should be able to fairly easily bike 60 miles. A reasonably fit person should be able to hike across most terrain for many hours because that is what our bodies evolved from. Not run, just hike.

Most of not all riders I know are fine with biking a metric, really the only limiting factor is the seat. Obviously the pace matters, but if we're just expending about the same as walking, then nah a metric isn't noteworthy. Like all riders I always loop an hour off my 50 miler then brag about doing...a fifty miler...

Of much greater concern is most Americans are physically unfit. As in, cannot walk an hour or two. In that sense, yes, you are nuts because you are part of a ever shrinking minority that can do 2-5 hours of anything that is slightly physically taxing.