Border Collies is a very active breed, walking is normaly not enough to keep them happy. I used to walk my low-energy Border Collie four times a day, between 45m-2 hours each walk. I also trained agility, obedience and tried a few other things like weight pull, tracking, and so on. Not all on the same day, but a 45 minutes traning + the four walks would keep him satisfied. :)
It is! But if you spread the walks out during a day it's seems less. Morning i would take him out 1,30-2 hours. Around 2PM i would walk him an hour and then take him out to pee, around 4PM and then walk again by 8PM for 1-2 hours depending on how much i trained that day.
If you train more mentally or let the dog work, that much exercise isn't needed. But i love walking. :)