Legally, the answer is "no."
With Universal Mail-In Voting (not Absentee Voting, which is good), 2020 will be the most INACCURATE & FRAUDULENT Election in history. It will be a great embarrassment to the USA. Delay the Election until people can properly, securely and safely vote???— Donald J. Trump (@realDonaldTrump) July 30, 2020
Congress does appear to have the power, in the event of an emergency of "changing the appropriate statutes, to change the general election date and as well the dates electoral votes are received in Washington and counted in Congress." However, given that the House is controlled by the party in favor of free elections, that wouldn't happen.
But it appears Trump soon will have one more Supreme Court justice on board if he does want to delay the election unilaterally. From today's questioning of nominee Amy Coney Barrett:
FEINSTEIN: On July 30, 2020, President Trump made claims of voter fraud and suggested he wanted to delay the upcoming election. Does the Constitution give the President of the United States the authority to unilaterally delay a general election under any circumstances?
BARRETT: Senator, if that question ever came before me, I would need to hear arguments from the litigant and read briefs and consult with my law clerks and talk to my colleagues and go through the opinion writing process. If I give off-the-cuff answers, I would be a legal pundit and I do not think we want judges to be legal pundit. We want judges to approach with an open mind.
The answer still is "no" legally and it doesn't take a pundit to know that. If she checked her search engine on a desktop, laptop, or smart phone computer, Judge Barrett would notice that the first Tuesday after the first Monday in November was set by statute in 1845 as presidential election day. U.S. Code now enshrines that occasion "in every even numbered year... as the day for the election, in each of the States and Territories of the United States, of Representatives and Delegates to the Congress."
Judge Barrett, being smarter than a fifth grader, could have taken the advice of the late First Lady, Nancy Reagan- "just say no." The Chosen One probably will not sign an illegal executive order postponing the election and if he does so, might get blocked by the courts. However, by nominating Amy C. Barret, Donald Trump did, knowingly, take one more step toward his goal of establishing an autocracy.