You could first define which elements that need to be updated, put them in an array and then after each timeout, update the next element in that array.
var i;
var cellsToUpdate = [];
for(i = 1; i <= 12; i++) {
var element = document.getElementById('t' + i);
if (window.getComputedStyle(element).backgroundColor == 'rgb(214, 255, 173)')
cellsToUpdate.push(element);
}
i = 0;
var interval = setInterval(
function () {
if (i >= cellsToUpdate.length) {
clearInterval(interval);
return;
}
cellsToUpdate[i].style.backgroundColor = 'pink';
i++;
}
, 300);
Check out this fiddle. Call the code above after you have changed the colors with the select dropdown. Don't forget to clear the interval when it is done.