Hi and welcome -- and good for you for taking the time to ask such important questions before you get a dog.
There's a fast answer to your question I am afraid, and I suspect it is one you already know: there is absolutely no way you could get a puppy with that schedule -- a pup cannot be left alone for such long hours. You would never have a housetrained dog as you need to be there full days at least for the first few weeks -- so you are right to be approaching this from thinking about an adult
.
The second aspect on whether it is fair for an adult dog? The answer again is *probably* - no -- or at least not without MAJOR adjustments/cost as you both have either long hours or unpredictable schedules -- the only way you could do this would be to use doggie daycare every day as if you are out 8:30-6:30 and your partner is away, this isn't 8 hours -- it is 10 hours. :yikes That's a horrific stretch and no way a dog could hold itself from needing to pee/poop all day every day for so many hours or even 8 tortuous days out of every month (imagine having to hold it for 10 hours yourself every day at work -- wouldn't you dread going to work?) -- and really you would only see your dog and your dog would only have companionship for a couple of hours a day before you'd go to bed. A dog needs at least an hour of daily active exercise -- vigorous walks and play, not just a trip around the block. If you eave home at 8:30 you'd need to allow at least 45 minutes extra in the morning to manage a dog -- feeding. walks etc. A cavalier cannot be outside alone all day in a garden either-- because being this alone is cruel: it can cause severe anxiety and damaging behaviour as dogs, especially this breed, are very social and intelligent and will be bored stiff and miserably lonely; it is too cold in winter; and this is a commonly stolen breed, so it is too risky.
You need to also consider what happens if your dog is sick -- it could not be left alone daily for 8-10 hour stretches. Be sure to research this breed carefully -- it has a very high risk of heart and neurological conditions at some point and so people do need to consider whether they could give the time to a dog needing regular medications. It's really critical for you to read not just surveys on what breed is right for you (which are generally pretty light and fluffy on real issues!) and read up on the breed, its real characteristics and its potential problem areas, including health. Cavaliers for example are NOT dogs that manage well left alone all day especially not a single dog. They do tend to gradually have significant health costs as they have endemic breed health problems that can be expensive (many of us have cavaliers with the debilitating neurological condition syringomyelia which requires medication every 8 hours or so or the dog can be left in pain, and such dogs really do need people around during the day to monitor them. Sadly this isn;t a rare condition -- three of my five lifetime cavaliers have had it).
All of this is not to say you could not manage an adult dog if you wished to make the arrangements and sacrifices. First off: you do need to recognise that getting s dog is a decade+ commitment and will totally change your social life. You cannot just head off for drinks or dinner after work, or take off at the last minute for the weekend, or vanish for the whole day on weekends when you have a dog that barely sees you anyway due to work schedules. This is not something people tend to think about, especially younger people who like the idea of the occasional companionship and imagine walks in the park and countryside and not the daily responsibility.
But assuming you are ready to make that major life change -- then you COULD work out owning a dog IF you come home daily for your lunch hour to walk your dog or hire a daily dogwalker or use daycare every day. I know people who do this -- but it is costly, just like childcare; and you need someone trustworthy enough to enter your house and collect your dog to take them out, if using a dog walking service.
And even then I would be asking -- is this really much of a life for the dog who sits alone without its actual owner, almost all day every day?
If you are really sure you want to give the time and effort to a dog, then do be sure to read up on the breed health issues and read our Considering a Cavalier post:
http://www.cavaliertalk.com/forums/showthread.php?10890-CONSIDERING-A-CAVALIER
and here's some good advice to consider on whether to get a dog -- some realistic idea of what you will need to be thinking about:
http://dogs.about.com/od/becomingadogowner/bb/getingadog.htm
http://www.petforums.co.uk/dog-chat/134055-thinking-getting-dog-puppy-realities.html
http://www.dogbreedinfo.com/beforeyoubuy.htm
http://www.petmd.com/dog/care/evr_dg_before_getting_a_dog#.UPvrLo6GjzI