Blizzard has been using a method to releasing patches. The best way to know is by raid fights on the PTR. Right now they haven't tested the Heroic fights but I know they will this month. Usually right after about a week or so, the patch will be released. Blizzard has also been using the 'end of the month' releasing method. Releasing a patch at the last Tuesday of the month. But rarely they'll use the first Tuesday of the month. So by looking where they are now, I would say
February 26th or
March 5th
Not saying this will be the dates. But if you need a source here it is for the last two expansions:
Patch 4.1: Tuesday April 26, 2011
Patch 4.2: Tuesday June 28, 2011
Patch 4.3: Tuesday November 29, 2011
Patch 5.0.4: Tuesday August 28, 2012
Mists of Pandaria: Tuesday September 25, 2012
Patch 5.1: Tuesday November 27, 2012
See the pattern?