"He may adjourn them to such Time as he shall think proper."

He is going to force them into adjournment and then make his recess appointments.

If they challenge and go to court he will cite Article 2, Section 3 that gives him the power in extraordinary occasions (like a global pandemic and a situation where all 50 states have declared disasters and the President is using war powers to manage commerce)... SCOTUS leaning 5/4 to the constitutionalists, will very likely side with the President.