Most people don't take 50 minutes to fall asleep unless they've just slept. It's been a while, but I believe the well-rested person carrying no sleep debt (according to Maas) takes about 20 minutes to fall asleep. If you're over-exerted (as most of us are), it should take less time than that. You just need to time this stuff properly, and get a sense for about how long it takes you to fall asleep.

Also, the 1.5 hours between sleep cycles isn't completely accurate - but it makes more practical sense to time it this way. Add to this, that not everyone has the same internal functionality, and you have a really complicated problem. Everyone needs a different amount of sleep each night, and I believe the cycles are different as well.

However, if you wake up around the times it suggests, you have a higher chance of feeling better. It doesn't ensure anything, but if you were going to wake up around that time anyway, might as well adjust 10-20 minutes for a better chance.