Some call it disc catching while others refer to it as Frisbee, but your dog will just call it fun. This is one of the most common park activities people enjoy with their dogs and for good reason. You both get to enjoy the sunshine and fresh air, you get some exercise, and you can meet other dog lovers as well.
Your Sheltie Tzu will always love to go for a walk with you no matter what time of the day or night it is so if you are at work all day long and cannot find the time until after dinner or right before bed, so be it. Your dog won’t mind. A walk is a walk, after all, and it is always fun to go for a walk with your human.