" We have been NU for a while"
If the Captain had been told that this was for over 2 minutes... By then it might well have been too late.
PF might not have known. It is difficult to estimate time PAST. Time from NOW is easier.
("When DID I put the egg in to boil ?" Or "I must take the egg out in 4 minutes time.")
When navigating, one was trained to note the TIME of an observation. ( "Was that fix 30 OR was it 35 minutes ago ?" meant that it was somewhat dubious.)
A change of sounds on the F/D may cause one to look around to try and see that " All is Well"... Nothing noticed ?
(The THS was following the PF's order to go more NU than usual ? Altimeters were moving too rapidly to read ? Was it only possible to NOTICE the "10,000ft" because of the change if the first digit?)