I think we've all been there. I can remember more than a few nights when I was attending Towson University that I stayed up into the wee hours of the morning preparing for a test that I should have been preparing for well in advanced. Sometimes things out of our control cause us to be late or unprepared. Maybe we forgot about the assignment, which might be a separate (but related) issue.
However, in most situations, I believe that we don't really feel a sense of motivation until things become urgent. Most people can bring themselves to study for a test the night before said test. Fewer people will have the discipline to begin studying a week in advance. Yet these are the people that will thrive. Once things become urgent, we have probably already waited too long.
A much better approach would be to do a little bit of studying at a time, well in advance. This will allow our minds to process and understand what we have studied; we will actually learn it! As the test approaches, we can simply review what we have learned, and walk into the classroom full of confidence.