Cary, LTP isn’t your all day power, it would actually be below that (I’ve found around 90% LTP is a good starting “all day” intensity). Think of it this way, riding at LTP towards the end of a longer ride would be similar to performing an effort at threshold when you’re relatively fresh. Just like riding at threshold is not sustainable forever, you’ll find trying to hold LTP at the end of a long ride will also be unsustainable forever. HTH