There's kind of a pattern here: Back in an August interview with Fox News' Brit Hume, Paul Ryan couldn't offer details on the budget proposal he and Mitt Romney would be promoting if elected because
"we haven't run the numbers" and also he didn't want to get too wonky, didn't want to get into complicated baseline issues, and so on.
Sunday, talking to Fox News' Chris Wallace, Ryan again ducked, dodged, and evaded Wallace's attempts to get him to be specific about the Romney-Ryan tax plan, culminating in the claim that "I don’t have the time. It would take me too long to go through all of the math."
Ryan is straight-up using his reputation as the Republican party's big budget wonk to get out of giving direct answers to any actual budget wonking questions. Because from his point of view, "I don't want to get too wonky" or "I don't have the time" are more palatable answers than "if I gave you details you'd see that I've been lying."