That's more than enough exercise for an adult dog, even a gundog like a vizsla.
They are a great breed, hardy, healthy, great with kids, good temperament etc etc. However.
Gun dogs are built to run and run all day with just a pork pie for lunch and then go again. They'll come to expect whatever routine you give them, so if you give them three hours, thats what they'll expect!
Without making a rod for your own back, an hour running off lead would be easily sufficient. Its better and more challenging for the dog to be off lead for an hour than on lead for three on a boring street. Your target dog is designed to run not walk!
Two hours of mixed exercise is all you need if you do it right.
Varying the walk's location - a different park, woods or fields each day stimulates their brains more too. Do that and the dog will rest more and be calmer.
You don't give clues to where you live, but a viszla isn't a city or town dog, so if you live in an urban area where the dog won't be able to chase, stalk and play flush birds or squirrels off lead, then its not really fair on it.
If you're in London, theres a show breeder who has 3 or 4 who walks each morning on Hampstead East Heath. Has a Range Rover with a private plate. Would talk vizsla all day long. Good for advice.
How are you going to get over the puppy stage, i.e., up to five months when the dogs bladder can last out being left?
The leaving the dog/puppy all day, even once a day is the bigger problem, especially if it becomes used to you or your partner being around, it will have separation anxiety on the day you're abandoning it (in its own mind)
Better to research dog day care or a dog walker who will pick up and take the dog for some hours before dropping it off again.
Leaving the dog of any age, especially a youngster, for more than four hours is unacceptable and unfair to the dog. Overcome that issue and its all good.