I've noticed my past few CR1s have cleared about 2-3 days ahead of the UDU window, but unless NF/NC was available at time of booking, have waitlisted the entire time up until that period. (For example, had one for Sunday, 5/29, just clear this morning, and it had been waitlisted since March.)

They're typically not buying me the "security" I'd like, but they are a bit more effective than UDUs.

Unless you definitely have other trips to apply them on before they expire (and those flights have open NF inventory), I wouldn't switch them yet.