An article on Drudge says that he can only do this until tomorrow at noon due to Senate rules.
Hmmm... I didn't think the Senate has a cloture rule. Senators can speak for as long as they hold the floor. They can yield for a point-of-order without yielding the floor, and then the point-of-order can continue for as long as the other Senator can go before handing it back to the controlling Senator.
-PJ
If this is a real filibuster, then Senator Cruz can hold the floor indefinitely. The Senate would have to invoke cloture in order to break a filibuster and as far as I know, cloture has not been invoked yet.
The longest filibuster in US history lasted 24 hours and 18 minutes. So it is likely that Sen. Cruz will yield the floor by noon tomorrow, not because of any Senate Rules, but because it would be likely be the longest filibuster in American history if he were still speaking at that time tomorrow.
The fact that the Senate rules require him to yield the floor tomorrow would mean that this is not technically a filibuster.