They don't. Here's an example from US History when they chose NOT TO ACT AT ALL:
Few Presidents have had a rougher time filling vacancies on the Court than John Tyler. His first maneuver, upon the death of Justice Smith Thompson, was to offer the position on the Court to Martin Van Buren, who was the leading candidate for the Democratic presidential nomination which Tyler hoped to claim for himself. But that crude effort to immobilize a rival was squelched before any nomination was made, and when Tyler named John C. Spencer of New York, the irate Whigs of the Senate rejected him. The President's next move was to offer this position to two Philadelphia lawyers apparently because he was impressed by the arguments they had just made in a case before the Court. When John Sergeant declined on grounds of age and recommended his fellow townsman, Horace Binney (at the same time swearing the President's emissary to secrecy about the prior offer to him) a tender was made to Binney, who declined for the same reason and recommended Sergeant, with a plea that his own declination never be disclosed. Tyler then twice offered the judgeship to Silas Wright, Democratic leader of the Senate, who twice declined. In desperation, Tyler sent the name of Reuben H. Walworth, Chancellor of the State of New York, to the Senate in March, 1844. When a second vacancy on the High Bench occurred, Tyler offered the position to James Buchanan, who declined, and then nominated Edward King of Philadelphia. On the last day of its session the Senate laid both nominations on the table. Trying once more in the last days of his administration, Tyler withdrew the King and Walworth nominations and sent in the names of John Meredith Read of Philadelphia and Samuel Nelson of New York. Nelson was confirmed and served on the bench for twenty-seven years, but the Senate did not act on the Read nomination. Only one of Tyler's ten tries was successful. (See "Robin Hood, the Supreme Court and Congress," in Yearbook 1978.)
As for trying to convince me this cloture abuse is constitutional, don't waste your time.
Trying once more in the last days of his administration, Tyler withdrew the King and Walworth nominations and sent in the names of John Meredith Read of Philadelphia and Samuel Nelson of New York. Nelson was confirmed and served on the bench for twenty-seven years, but the Senate did not act on the Read nomination.The cloture abuse in the 108th Congress did not occur in the last days of GWB's administration. Now, of course, there is a time factor in there somewhere. It is sill to say that a nomination offered on the last minute has to be acted on. Or last day, or final week, and so on. I don't where the line is, that it appears the Senate's acts are at odds with the balance of powers scheme the Constitution is meant to obtain.