On soft ground, up to 45 minutes at a fair pace with plenty of stops. She is off lead and often investigates away and then rejoins me a little later. Just worrying a little re. possible future joint trouble. She loves running and accompanying me and is very fit.
We do about the same with our flatcoat x golden retriever who is about the same age. I think I have read that 18 months is the earliest dogs can compete in canix and things like that, so I think doing short runs where the dog sets the pace are fine.