'will' in this case means 'are happy/willing to' - it's blaming the dogs, like their behaviour isn't good. eg: you can say 'My son won't eat vegetables'. It doesn't mean future, it means 'he's unwilling to/he refuses to' :) He's home, or 'I'm home' is like a state, but 'at home' is your location, if you are taliing to someone else on the phone. :)

You wouldn't have been wrong, Cinzia. English grammar is very flexible, and allows for very many different constructions. "Explain to me why when John is at home, the dogs sleep in until almost seven but when he is gone they are up at five or five thirty EVERY morning!" would have been completely fine. I don't really agree with Keith (sorry Keith!) about the "will" here either. While it can have that meaning of intention, in this sentence it is being used to describe habitual behaviour. But the meaning is not really at all different from the answering "when he is gone they are up". Some English writers like to avoid repetition wherever possible. There's even a pair of terms for this : "elegant variation", and "inelegant variation". Rather than chasing very fine or non-existent differences in meaning here, it might be more helpful to see that you have a range of forms of expression available. Oh, and of course you could have used "John is at home". These are simple alternatives. "John is home" is just a little more informal, but either is entirely acceptable, and there is no difference in meaning in this context*. This might help : https://forum.wordreference.com/threads/expressing-typical-behaviour-using-would-and-will.3255599/ or https://ell.stackexchange.com/questions/33930/typical-behavior-and-habits-via-the-present-simple-and-will https://fergus.wordpress.com/2007/08/24/elegant-and-inelegant-variation/ *"at home" is a state, so if somebody has just arrived you wouldn't easily use it. Then you would go for something like "Peter (or Jo or Daddy, or whoever) is home. " Or "Peter's back", quite often, if the subject has returned to a shared base.

When John is home the dogs usually sleep until 7:00,but when he is away they are up at 5 or 5: 30.