To write the best version of whatever it is you are working on, you’ve got to find some way to care about it. For some folks, this is a grade or a paycheck. For others, it will be the idea or issue itself. In my experience, caring about a grade or a paycheck does not produce the same quality of work that caring about the project itself does.
If you are writing for yourself, this is easier to do. If you are writing for an assignment, you have to figure out what in the parameters of that assignment you can care about enough to spur your best thinking and effort. Writing about what you care about is almost always a better tactic than writing about what you think a professor or boss cares about. The first question you should ask yourself when starting a new project is ‘What about this do I care about the most?” If you can identify and focus on that, you are off to a damn fine start.
There is no ideal time to write, but there is an ideal time for every stage of the writing process. In general, brainstorm and draft when you are well-rested, well-fed, and generally feeling good. Your creative and associative mind works best during these times. Most people who like to write in the mornings do so because they have slept, eaten, and caffeinated.
When you are tired and lower-energy, edit, proof, and revise. When you are somewhat fatigued, your creative mind abates and your critical, analytical mind is more active. You are more likely to identify logical mistakes and see the faults with what you’ve done. As strange as it sounds, only working on your project when you are feeling your best doesn’t necessarily produce the best work.