Just happened to me - one ticket 4 sectors, all CX/KA, all except first sector confirmed, deadline Jan 31; waitlisted another flight for first sector, shortly the new flight clears, agent calls and deadline becomes Jan 26 (while I continue waitlist for the original first flight); called later on to change my second sector, available thus immediately confirmed that, and deadline becomes Jan 31 again.

I don't know if I should trust that, so maybe to ticket it by Jan 26 to be safe?