If you choose to apply for federal student aid (which we recommend you do), you must complete and submit your Free Application for Federal Student Aid (FAFSA) as soon as you can—after January 1st. Your chosen schools will use the results of that FAFSA to build an award package for the fall of the same calendar year and the spring of the next calendar year.
You need to complete and submit the FAFSA for each year that you attend school. Three years at school means completing a FAFSA three times.
The government accepts and processes FAFSAs well into the summer, but the schools you apply to will have more aggresive timelines. Be aware of your chosen schools' financial aid deadlines ahead of time and schedule yourself to meet them. (It is not uncommon for schools to require additional forms, as well.)
The graphic below represents the timetable described above.