There probably won't be a chapter until next week.
Chapter 312 officially was released on
12/26 in issue #4-5. It's a double issue which means that they put two issue numbers on a single issue, so that they can take a week off without disrupting their count.
Chapter 313 officially comes
with issue #6, which will be released on 1/9/13.
Due to the way that the industry printing and distribution system works, copies of a magazine can be available up to 5 days before the official street date. Those early copies are what scanlations usually get made from. That's why we got "this weeks chapter" last Friday.
When there's a double issue, the distribution time tables tend to change. As such we could get a chapter today, in which case there would be no chapter next week, or we could not get a chapter until next friday. Or any time in between.
In general, any time you're curious as to when scans are most likely to show up for a new chapter, just go to
http://kc.kodansha.co.jp/magazine/index.php/02065/next check the date of the next issue (it's in year/month/day format and should be fairly easy to pick out even if you don't know Japanese) and subtract 5 days.