On the accounts page where it shows how many days of sub you have left, the hours and minutes aren't displayed, so the second you sub for any amount of time, it automatically drops to one day less, but you'll still have the '0' day where you're still subbed but it won't tell you how many hours are left.
If you haven't been playing for a while, there's a reasonable new deal active until the end of the month, where for 39.99 you get the expansions through SoR and 2400 cartel coins (in game real money currency conversion), plus two months subscription. It's not a bad deal. Sor on it's own is 20.00, the subs would be about 30.00 and another 20.00 or so for the cartel coins, so you save a bunch. Even if you already have SoR, you can save 10.00 off the coins and sub fees.
I get the most enjoyment out of building new toons and running them through the storylines, but my 8 mains (one for each storyline) grind endgame ops and PVP so I have the cash to bootstrap the new guys and get them all the cool outfits and gear right out of the gate.
And yeah, the x12 XP was just if you preordered SoR last year and only ran up until the early release. It was intended to allow people to just do the main storyline missions, ignore everything else and get to max level by the time SoR dropped...which it did, and it was awesome, except for those thousands of players who used it and didn't bother to learn anything about their classes or roles, but who now flood engame.