whether 01/05/2012 11:28:42 represents january 5th 2012 or may 1st 2012, only you can say
but to do anything with it, you must convert it first to an actual mysql datetime, and you need to use the STR_TO_DATE function for this
then, once that's working, you can use UNIX_TIMESTAMP to convert it to an integer, if that's what you were after