Check out the mktime function:
http://www.php.net/manual/en/function.mktime.php
int mktime (int hour, int minute, int second, int month, int day, int year [, int is_dst])
i.e.
date ("d-m-Y", mktime(0,0,0,1,1,1970))
You will need to format the timestamp field using substr.
This may help,
David