Converting Twitter date format to standard Excel date format to use with WEEKDAY function

Hello Excel prodigies,

I've been trying to use the WEEKDAY function on a series of tweets I managed to get into Excel, because I want to be able to see the corresponding day of the week for each tweet. However, it seems Excel cannot properly recognize this format 2012-12-16T21:08:09Z as a proper input in the "serial number" field of the WEEKDAY function so I guess I would have to somehow manage to transform it into 16/12/2012 format. Can any Excel expert teach me how to do this the simplest way possible? I attached what kind of table I need.

Gratefully yours
D