Sure, having to work on Christmas Eve is not so fun. Everybody from the Virgin Mary might have something to say about that.
But consider the work the Senate has before it -- A treaty to limit nuclear weapons and a bill that funds the federal government. Spending the week before the birth of the Prince of Peace thinking about a peace treaty seems okay to me. And the other bill (with the terrible name of omnibus spending bill) contains some pretty needed stuff, too. Sure it's got some "pork" and sure it needs a full discussion, but that bill includes things such as health care for poor people, projects to prevent the flooding of towns and money for a hospital emergency room. The Jesus whose birthday is coming up, said he came to "bring good news to the poor." Again, spending some time before Christmas talking about how we help poor people seems like an okay use of anyone's time, even United States senators.
The two senators who criticized the Senate schedule have backed off their comments a little bit. And they're certainly welcome to vote against these bills if they choose. But hiding their opposition behind inflammatory religious language seems to miss the point of the holiday they say they're defending.