Libby's peanut gallery would have been furious if he had been locked up for a day, so Bush had to act quickly. If Libby were going to squeal, he would have done so at sentencing at the latest. He won't say a word based on conditions as they are now. Of course, if he's found liable for $20M in a civil suit, well that might change his thinking, but I really doubt it.
Remember Bush still has the option of pardoning him after Libby's appeals run out, too... :-/
Cheers,
Scott.