This is indeed a good strategy because when you are at your freshest your mind is fresher you will be able to think more reasonably and you will be more focused.
Bananas have been known to help you focus during tests and while working because of the fiber it help's keep your cholesterol and blood pressure in check, and help ease inflammation.
Orange Juice works as well they work pretty much just like bananas.
It is bad to try doing anything when you are tired because your body is starting to relax it's self so that you can sleep and be refreshed, your mind also relaxes, that's probably why when you get tired you find yourself laughing more than normal, you may even have slurred speech depending on how tired you are, your eyes start to shut causing your vision to blur meaning an obvious lack of focus, and you may even find yourself staggering around and running in to things when trying to walk.