Legend - you'll really see the benefits of working with a qualified trainer on specifics like this (duration sit or down stays). A trainer will help you learn what works for YOUR dog (both temperament and age related) and you won't be working with generalized information. Each dog is different and having a qualified trainer to work with is priceless - because the trainer will teach you how to not only teach/execute the command to your dog, but can help you with the resulting 'reaction', should there be one you need to address.
Once you get with a good trainer - you'll be surprised at how much of your dog's behavior is a direct result of YOUR training techniques - even those you think you are currently doing 'right'
This won't be a few short weeks and you're done either - you do know that, right?
