Just got my legacy status on Saturday. Here's the deal:
Nobody knows an official date when the servers are going down, probably not even SE.
Nobody knows when closed alpha, closed beta, or open beta is going to start, probably not even SE.
(this lack of a definitive date is a good thing, doesn't tie the XIV's devs hands to rush out a crap program)
The legacy campaign requires you to be subscribed for 3 consecutive months, aka 90 days(since some months have 31 days in them)
Further more Yosihda San said it will probably require a month to transfer account data.
And he also said he'd like beta(s) to run along side 1.0 until its time to migrate data to 2.0

If 1.0 runs until November 30 and the servers go offline on December 1st, in preparation for the January unofficial launch date, then your 90 day mark is October 28th. IF the game (1.0) is still up and running, there's a pretty good chance that since you paid you'll receive your status. However....

You cut it awful close, I wouldn't expect it if I where you.

The legacy campaign dates were dates associated with a time frame they KNEW players would meet. Basically everything past that date was up in the air, coin flip, etc.