Your date format is wrong. The format for months is "MM" (not "mm", which are the minutes), and the 24-hour format is "HH" ("hh" is for the 12-hour am/pm hours):
[dateFormatter setDateFormat:@"MM-dd-yyyy HH:mm:ss"];
Also, as @Flexicoder mentioned, you should specify a "locale" to be independent of the user's locale settings:
[dateFormatter setLocale:[NSLocale localeWithLocaleIdentifier:@"en_US_POSIX"]];
(See http://www.flexicoder.com/blog/index.php/2013/10/ios-24-hour-date-format/ or What is the best way to deal with the NSDateFormatter locale "feechur"?.)