I always stick to the 5 min rule too, better safe than sorry IMO.

I also cut down my pups playtime with Maddy (one of my older dogs) as she would just keep going 'til she collapsed i'm sure and there is a lot of manic bounding about too as you can imagine. Just because a pup would LOVE to be out walking everywhere with you for hours on end, doesn't mean they should be. JMO of course.