Hook any event and calculate time execution

Question

I have few buttons on screen. I need to calculate execution time when any ui element is pressed, but without adding that to every button. I have function that catches only View Controller touching.

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event
{

    NSString * strLoad = @"";
    for (int i = 1; i <=100000; i++) {
        strLoad = [strLoad stringByAppendingString:@"add"];
    }
    NSLog(@"touchesBegan");       
    NSTimeInterval delta = ([[NSProcessInfo processInfo] systemUptime] - [(UIEvent*)event timestamp]);
    NSLog(@"time %.2f", delta);
}
- (void)viewDidLoad {
    [super viewDidLoad];
- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}
- (IBAction)btnMetadata:(id)sender {
    NSString * strLoad = @"aBC";
    for (int i = 1; i <=500; i++) {
        strLoad = [strLoad stringByAppendingString:@"add"];
    }
}
- (IBAction)btnGenerateCrash:(id)sender {
    NSString * strLoad = @"aBC";
    for (int i = 1; i <=5000; i++) {
        strLoad = [strLoad stringByAppendingString:@"add"];
    }
}