then the pilot monitoring should have had full attention on the engine instruments
I may be being a bit pedantic but if the PM had "full attention" on the engine instruments he or she would not be able to comply with the Boeing recommended SOP's for this phase of flight.
Maybe you meant that the PM should be focussing much of their attention on the engine instruments?
With your rather generous 3 seconds for recognition I think you are departing the runway with full thrust on one and none / reverse on the other if you are below 60kts.