you can't apply for visa extensions in Gilgit until 5 days before the visa expires. as Beck says, the process in Islamabad is more complex, we ended up giving up and are now going to try in Lahore, where you don't have to go through the interior ministry.
Also we met a german guy in Islamabad last week who had gotten two extensions; the first took 19 days to get a 30 day extension, but the 2nd took 2. It seems to be a bit of a lucky dip.
