No school will have a deadline for FAFSA before it is available in Dec. Some schools may have a deadline for priority consideration for financial aid, but again it will not be before Dec. (for the past few years the FAFSA was opened on Oct 1, so some schools may still have old deadlines on the FA pages). Just complete it as soon as you can.
If a school issues ED before December, they may not be able to give you the financial aid package (like a Pell grant amount), but schools that also require CSS, they may be able to tell you some of the financial aid as the CSS should still be available in Oct.