So then, I suppose the question is, how long would your typical antitrust case take?
I've never litigated an anti-trust case (and hope never to do so!)... but most of your normal civil cases can take up to a year or more just to get to trial, but could sometimes be much longer. I was actually a contract attorney on a simple credit card case that had been on the docket since 2007-ish a while back, actually.
It depends on where you file your suit, too. The Brees/Brady/Manning suit was filed in a federal court up in Minnesota... Don't know how busy that district usually is. For example, in my district (Western District of Missouri), we have so little action in the federal courts here that everything could done pretty quickly. Additionally, they filed there purely for strategic reasons -- Judge Doty, a judge in the district, has apparently been very friendly to the players in past negotiations & cases and Minnesota is a very union-friendly state... but Judge Doty hasn't been assigned to the case. I'm sure the NFLPA will likely try to get it reassigned, which of course adds time to the case.
Of course, remedial measures (i.e. preliminary injunction) will be ruled on before the case ever goes to trial. And finally, they're asking for class-action status, which is just going to add more time to the case.
They could be in the legal muck for a loooonnngggg while.