How long (in minutes) is considered a "long" walk?

If you're moving at a good pace, I'd say an hour or more is a long walk. However, I personally prefer using intensity as a measure. Especially for higher energy dogs, the greater the intensity of the activity, the 'longer' the walk. Twelve minutes is a short amount of time, but I can run my dog on the bike for about 3 miles in that time and afterwards she is exhausted. Conversely, I could walk for an hour and even if we cover more distance it won't even take the edge off her energy.

If you're discussing walk length with a client, be sure to discuss what each of you considers long, and what factor is the most important to each of you.

I consider 45-60 minutes a long walk.

Since Rover requires at least a 30 minute walk I consider anything over an hour a long walk. Depending on the size of the dog I always try and decide how long I should go so the dog really benefits from it!