Maybe the clerk can confirm this, but my understanding is that amendments can be moved at any time during clause-by-clause consideration. My understanding of this particular clause in the routine motions is that substantive amendments be moved 48 hours before the committee's clause-by-clause consideration so that.... They know the general direction of the other committees and can propose responses.
I'm not suggesting that 48 hours before is a bad amendment, but I don't want to be restricted on the basis that an amendment has been moved and a subamendment or a friendly amendment might have to be moved to deal with that particular issue. You're not precluded, I think, from the normal practice, which is to move a subamendment during clause-by-clause consideration. I do it all the time.