HI
Know this is an old thread, but thought I would reply in case anyone was still about (I'm new here!)
I've never had a Viz, we are considering it hence me visiting

But I have had several springers.
I don't know whether it applies to a Viz, but what I discovered pretty quickly was you will never tire a Springer by walking as they will literally go forever! A quick power nap and they are back on it. But I found getting the springers mentally tired, was more important than getting them physically shattered (as I say virtually an impossible task)
So I found a half hour walk which included some tracking, proper lead walking (ie where they are working to follow you, not pulling you down the street) some retrieval, followed by 5-10 mins run round; tired them far more than a three hour run off the lead round woods etc where they weren't being mentally worked. Walks out were also more tiring than round the garden, due to new smells, sensory experience etc
Something else worth seriously considering if you work is getting a treadmill for you dog - for those that do need a serious energy release and you don't have time before work! You can also get doggy backpacks for those who need something a bit more challenging!
Lastly saw the dog whisperer take a Viz out with his roller blades the other day - that looked FUN!