Thorough testing in the digital environment combined with iterative implementation solves the problem quite well, given that any issue (of which there should be few if testing is reasonable) that can't be quickly solved in the Prod environment can be rolled back with a quickness and retested on the Dev side. Maybe instead of proper planning for the application architecture they spent all their money on the timer and the new promo video.
DevOps?
But on a serious note, that is a very short sighted move. Its a good way to lose sales for those x days that nobody can look up anything on the website. I know if I had a customer service issue I'd be pissed I had to wait for their countdown to look up an email address or phone number to contact them.
By all means. Have a kickoff countdown. But as PART of the website, not the whole damned thing.