Substantive motions do require 48 hours' notice for the committee.
Also, the chair of a committee, much as the Speaker in the House, can request that the motion be provided in writing—I would venture to say, in front of the chair—to be able to evaluate whether the motion is of a substantive nature to the subject matter presently under way or whether it's outside the scope of what the committee is dealing with.
Motions, if they deal directly with what the committee is presently discussing, can be admissible outside the 48 hours' notice if they relate directly to what the committee is studying. That said, as I mentioned, the chair would require that in writing to be able to evaluate it.
The committee can hold extra meetings, in addition to the meetings they have scheduled. That would be at the discretion of the committee, to advise the clerk when and where. Conference call meetings are typically very difficult to organize.
The committee could also, by unanimous consent, waive the 48-hour notice requirement or could agree to a compromise whereby the notice requirement would be, let's say, 24 hours as opposed to 48 hours. But that again would require unanimous consent.