EICAS would have brought up the ENG FUEL FILTER L + R and then possibly gone into the by-pass stage.
You would have to ask how fast an impending fuel bypass event progresses...
The impending bypass alerts are Status Messages. Cautions, Advisories and Status messages are inhibited below 800' (someone reminded me in an earlier message thread about inhibits)
If fuel flow was being restricted/slowed, is it conceivable that the engines could sustain idle power (for a considerable time),
but not above-idle thrust? The 8 seconds between both engines not responding to increased thrust lever input might not be such an important factor here.
Rgds.
NSEU