Who is the Attorney General?

Neal Katyal and George Conway have an op-ed in The New York Times arguing that the appointment of Acting Attorney General Whitaker is illegal and that any actions that he takes are null and void. I want to make one observation about their argument.

The Constitution sets forth a way to fill a vacancy created when a Cabinet member resigns, dies, or is fired. The President can make a recess appointment under Article Two, Section Three. In 2014, the Supreme Court held in Noel Canning that the Senate gets to decide when that body is in recess and, thus, when the President can make a recess appointment. This means that if the Senate was in recess yesterday, Mr. Whitaker's appointment is lawful but will expire at the end of the year.  But was the Senate in recess yesterday? The Senate was not in session yesterday. but I am unclear whether the Senate's adjournment on Tuesday (scheduled to last until Friday) is a recess.

If the Senate was not in recess yesterday, then I'm having a hard time understanding how the Federal Vacanies Reform Act does not present a constitutional problem as applied to Whitaker's appointment. What is the point of the Senate staying in session to prevent recess appointments if the President can make the same pick under the Act? Moreover, the Act in this instance may be increasing the scope of the President's temporary appointment power beyond what the Constitution would give (less than two months), and I'm not so sure that Congress can do that.