There are many answers for similar questions, just posting this answer incase you haven't found it yet
NSString *inputString = @"2013-05-11 05:54:07.589698";
NSDateFormatter *dateFormatter = [NSDateFormatter new];
[dateFormatter setTimeZone:[NSTimeZone timeZoneWithAbbreviation:@"UTC"]];
[dateFormatter setLocale:[[NSLocale alloc]initWithLocaleIdentifier:@"en_US_POSIX"]];
[dateFormatter setDateFormat:@"yyyy-MM-dd HH:mm:ss.SSSSSS"];
NSDate *date = [dateFormatter dateFromString:inputString];
[dateFormatter setDateFormat:@"HH:mm:ss"];
NSString *timeString = [dateFormatter stringFromDate:date];
NSLog(@"%@",timeString);