Lakebum,
This is one of those things that, over time, you will learn what works best for you, and your coach, your driving techniques, you're standard of braking, and much more, that will all co-inside with the use of that Exhaust brake. They work outstandingly. You will extend the life of your service brakes by thousands and thousands of miles with the proper use of that exhaust brake. Mine is on almost 27/7 when I or the wife is driving.
Because it's 1.5 second reach for the switch to turn if off, I just leave it on and, when not needed and want to coast, it's flipped of in a matter of a second or two. Then, it's flipped back on when needed or, will be anticipating a need for it. Good luck.
Scott