That would be at the discretion of the committee.
One of the reasons why the text in bold was added--that 48 hours' notice be calculated in the same manner as for the House--is to reinforce the idea of it not being 48 hours in the pure sense of hours, but rather in the sense of two days.
That being said, you are correct, Mr. Reid, in that there are times during the 24-hour day that I'm not checking my BlackBerry--