Если не 2700, а 2500
<button class="perk_border">But1</button>
<button class="perk_border perk_border_g pr_gr">But2</button>
<button class="perk_border perk_border_y">But3</button>
<div id="clicks"></div>
<script>
B=setInterval(function atak()
{
document.getElementsByClassName("perk_border")[0].click();
document.getElementsByClassName("perk_border perk_border_g pr_gr")[0].click();
i++;
if(i == 8) {
document.getElementsByClassName("perk_border perk_border_y")[0].click();
i = 0;
}
},2500), i = 0;
document.getElementsByClassName("perk_border")[0].onclick = function() { clicks.innerHTML += "1"};
document.getElementsByClassName("perk_border perk_border_g pr_gr")[0].onclick = function() { clicks.innerHTML += "2" };
document.getElementsByClassName("perk_border perk_border_y")[0].onclick = function() { clicks.innerHTML += "3" };
</script>