Do you mean how long it will take because you need the value in the next line like this:
int x = 0;
x = x + 1;
turn(x);
then the answer is simple: Java will not execute the next line while the line before is not processed.
If you mean how much runtime it will take:
It's just a addition and it'll not take much runtime.
But better use this:
int x = 0;
x += number;
//or if the number is 1 you better do this;
x++;
in this cases Java only needs to call the value x one time, not two times like in your case