Clicks a button after t seconds

schedule_button_click

setTimeout(  
  function () {  
    //Depending on your button, you can also use getElementById 
    var x = document.getElementsByClassName("_42ft _4jy0 _11b _4jy3 _4jy1 selected _51sy");  
    x[0].click();  // x[0] gives us the first button with same class name  
  }, 3000   //timeout in milliseconds
 );