It is a continuing online application with no due dates. That said, congress sets the rating / budget on how many slots can be picked up throughout the year. As an MS-1, you need to submit undergrad transcripts and
follow the link. You can always apply for the scholarship to take place at a future semester, or as early as the upcoming fall.
They do take a few things into account: veteran status, GPA, cost & time obligation for schooling. I would also keep in mind, that if your application is declined for the scholarship, you have 1-year from the time of your application to resubmit. This would mean that at this time every single year, you would be applying based on the number of positions available around this time period (just something to keep in mind).
Best of luck