When is the apparent winner of a presidential election actually designated as the President-Elect?

Well, my least favorite source, wiki, says, speaking of the apparent winner of a presidential election, "There is no indication when that person actually becomes president-elect."

https://en.wikipedia.org/wiki/President-elect_of_the_United_States   

I beg to differ, and couched in the beg is my complaint that wiki says of itself that it is not reliable: 

https://en.wikipedia.org/wiki/Wikipedia:Wikipedia_is_not_a_reliable_source.

Wiki is a collection of self-appointed editors, on whom we trust to do necessary research, and their commentary in the first eiki citation above indicates just how poorly they do that job, because the answer to their question, "there is no indication..." happens to be in the Constitution, Article II, Section 1, clause 3 [Amended by the 12A]: "The President of the Senate shall, in the Presence of the Senate and House of Representatives, open all the Certificates [from the previously mentioned vote of the Electoral College], and the Votes shall then be counted. The Person having the greatest Number of Votes shall be the President [when he is later inaugurated the following January, and until then, he IS the President-Elect, officially declared by the President of the Senate who is the current Vice President], if such Number be a Majority of the whole Number of Electors appointed..." That happens after the Electoral College vote, which is established by law to be the first Monday after the second Wednesday of December of a presidential election year.

If I can do that research, and figure to begin with the Constitution rather than a collection news articles, why can't wiki? Because it's not reliable, and says so, that's why.

we dont know yet

Well it is the difference between the constitutionally required deadline and the actual real world practice. The constitution requires the electoral college to vote and the winner of that vote is the president elect. However, we already know that Joe Biden is the president elect. He won the election. No one ever waits until the electoral college vote to begin the transition period. All that would do is cause a delay in the new administration being prepared to do it's job. 

What you so easily pass off as "real world practice" is nothing but the fourth estate's usurpation of the first estate's documented privilege, as if "practice," aka "tradition" were so bloody important. But the fourth estate is the fourth, not the first, as if the United States of America were just another country, even though it managed to accomplish what no one in the eighteenth century figured would ever happen: the overthrow of the notion that monarchistic Europe dictated the world's convention. We, the people of the USA are exceptional, regardless of Oba'a and his claim that we're ordinary. The Constitution even dismantled the notion of estates. Who is, literally, the first estate today, if one want's to be harnessed to that anachronism? The people, not the government. "We, the people... establish Justice... and the Constitution." Not government. Yes, we, the people elect the President, but there is still a protocol established in writing just so the people can depend on one voice to offer the good news of the person of the Presidency: the current Vice President, not the NY Times, or even the NY Post, the nation's first newspaper.

no, the president elect is only official after the electoral college votes. But since we already know how they will vote, that is a formality. Pretending like Joe biden isn't the president elect is dangerous. Both because it will get millions of people to reject the outcome of the election as fraudulent, even though it isn't. and also because it means that when biden takes over in january, his team will be much less prepared to take over because trump has blocked his team from having access to the information and resources they need for the transition. 

Trump is endangering american lives by pretending reality isn't reality. 

The reality, my history-ignoring friend, is that several states are in automatic recount, and several others with lawsuits filed in court, the which process will conclude one way or the other, but in the meantime, until the Electoral Votes, Dec 14, you can project all you want, but the projection is not reality until Dec 14. Get it?

so your argument is that there might be not one, but several, monumentally unlikely things that could change the course of the election? The odds of that are a million to one. And because of that million to one chance that Trump could still win, we should prevent the biden team from preparing to do their jobs, thus potentially endangering national security and american lives, just to protect trump's ego?