It appears the online code is for the same dates as the contest.
I can mail away for 33 codes or purchase $5 boxes for codes....but I can only use one of these per day and it costs me money.
I can obtain an online code that is valid for ALL days (once per day), spending no money.
I'm not sure why, other than for kindness or a legal purpose, they would set it up this way.
You can only claim your online code starting Oct 29 whereas the Taco/mail-in codes start Sept 26.
Considering they'll be picking a winner about every 15 minutes throughout the contest you're going to want to get your entries in early.
Where the heck do you get postcards these days?