OK ... forgot about that. but what prevents the EC from acting the next day ?
Because the votes haven’t been counted. You’ve got to remember it’s a big country, and it’s a de-centralized country. Each state legislature is tasked with running their own elections within a very loose framework (basically the date and the federal offices on that date), so each state runs things differently, and most aren’t terribly efficient. And with recounts it only gets worse (AZ-2 is expected to finally be certified today). And all that MUST be done before the state sends its EC representatives. And the EC might not actually give enough votes to one side for their to be a winner, so they need time to go through multiple ballots and all the other stuff that can happen to finally actually elect a president.
You need to remember, our government is actually specifically designed to NOT be efficient. Gridlock is built directly into the very structure. You want efficiency. You want efficiency, it’s like wanting water to roll uphill. Not gonna happen.