Let us say i've two functions in functions.php in Wordpress.

function1(){
  // it takes 2 minutes to finish whatever it does
}
function2(){
  // it takes 3 minutes to finish whatever it does
}
function1();
function2();

My real question is how would be the functions performed?

1.First is performed function1 so when it's finished begins the execution of function2, therefore the final time is going to be a few minutes?

2.The execution for begins in the same time frame and also the final time is going to be 3 minutes?

Hope you'll understang my problem, thanks.

a few minutes - PHP will run the functions one by one, instead of the kind of JS which will run them at the same time.

I'd question what takes 2-3 minutes to process in PHP though? Most browsers will break after thirty seconds of PHP execution, so a few minutes could be method to lengthy...

so far as I understand function2 begins after function1 has finished performing... therefore the total execution time is a few minutes inside your situation...