What about the February LSAT?
What about it? Oh, you mean, what if I'm thinking about December and then thinking, Well... maybe not so much?
Here're some thoughts:
You can take the February test for Fall admissions, at least at most schools in Southern California (I have less direct experience with schools outside this area, but I'm confident that SoCal schools aren't unique in this regard).
The thing is that you'll guarantee by doing so that your application comes in late in the cycle. Here's what that means for you:
Being late in the admissions cycle is probably most detrimental to people at or slightly above the median admissions standards. Late in the cycle, there will simply be more applicants with similar numbers, and schools just can't admit them all. So, earlier is better, but that doesn't mean that a later application will disqualify you.
Qualified candidates are as well-qualified in November as in February. They're just competing for fewer open spaces as the cycle wears on. But schools don't finalize their acceptance offers ahead of their deadlines. Thus, you'll properly picture the relationship of timeline to admissions chances by picturing a 5% drop in your chances by applying in February rather than in November.
Obviously, such a formulaic response oversimplifies the matter - law schools are actively engaged in seeking the best candidates for their schools, and offering acceptance letters to the most-qualified candidates that they believe will accept their offer, so the whole relationship cannot be correctly boiled down to any mathematical formula. But this picture is much, much closer to the truth than to say applying later in the cycle removes your opportunity for admission.
With rolling admission, if you're in early and just above the median with strong letters of recommendation and an awesome Personal Statement, you may have an easier time getting an acceptance (schools know they're going to admit lots of people at or very near their median, so they may call you a presumptive admit early in the cycle, even though they might just not have room for you later in the cycle).
Of course, in these heady days, with applications down so much across the board, those normal rules may not fully apply as schools are more desperate to fill seats...
It also might help to think about it this way:
If you're preparing for the December test and thinking you might postpone until February, I'd say that generally, if you're confident of doing more than 4 points better by waiting, you should wait.
Of course, you should also consider waiting a whole extra year (if your life will permit it) so you can take that higher LSAT score into an earlier spot in the rolling admit process.
Just a few thoughts; I hope they help you plan.