Oh goodness, I'd be changing vets if mine was as casual about such a problem. The more the diarrhea goes on, the much greater chance your puppy will become dehydrated. Is he drinking a lot to replenish all those lost fluids? When you grab the skin on his back does it pull away easily? If it's tight then he's dehydrated and definitely a serious matter.
Rectal temperature of a dog is 99.5 to 102.5 F. A good thing for anyone to check if their dog isn't feeling well.
If he's still playing and otherwise acting normal, that's good to hear but don't wait until Friday to take him in.