For what it’s worth, my observations, which are just anecdotes, are that Willie’s greeting behavior varies tremendously based on how long we have been away. When we returned from New Zealand, after being gone for 3 weeks, he ran between Jim and I, whining endearingly, flipping in circles, licking our faces raw . . . a very, much more intense greeting than if one of us had been gone for a day or two. Do you observe that your dog greets you differently when you’ve been gone longer? However, there was no statistical significance between the dogs behavior if left alone for 2 or 4 hours. In brief, they recorded the behavior of dogs left by their owners for 30 min, 2 hours and 4 hours, and found that if the dogs had been left alone for 2 or 4 hours they greeted their owners with more ‘intensity,’ and were more active and attentive, than when the duration of separation had only been 30 minutes. One is that the dogs perceived a separation of 2-4 hours as not being particularly different, but very much different from a 30 minute separation.