In Objective-C, you commonly nead to convert a string to an NSDate object.  A simple way to do this is using the NSDateFormatter object.  It provides the dateFromString method which converts a string into an NSDate object.  You do, however, need to tell NSDateFormatter the format the date will be in.  See below example:

NSDateFormatter *df = [[NSDateFormatter alloc] init];
[df setDateFormat:@"yyyy-MM-dd hh:mm:ss a"];
NSDate *myDate = [df dateFromString: myDateAsAStringValue];

NSDateFormatter uses the Unicode Locale Data Markup Language to determine the date format.  You can view specific formatting options on the Unicode website.