NSDate

 I have written this code on application Resign Active

   NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);

    NSString *filePath = [[paths objectAtIndex:0] stringByAppendingPathComponent:@"file.plist"];

    NSDate *currentDate = [NSDate date];
    NSMutableDictionary *d = [NSMutableDictionary new];
    [d setObject:currentDate forKey:@"my-date"];

    [d writeToFile:filePath atomically:YES];