If you want to keep the aroma and flavour of the hops I would expect you would need to keep the whole heat extraction process to be under 20 minutes. Anything longer than this and I would think you would break down the lupulus of the hops too much and just be left with bitterness. I don't know about the safety of it though and you should probably research it more as although hops are safe for human consumption in beer and such, if a dog eats a few hop flowers it will be dead in 24 hours from malignant hypothermia.

So would that be a brew in bag process?