IMHO...
And to answer the original question
You start your lever movements at DA
If you sink transiently below DA during the
GA its still a pass on the IRT
The DA is the point of DECISION not a
point below which you musnt sink
You START to go around when the DECISION
is made
However in the case of an Asymmetric commital Altitude (I use QNH) go around
being lower than DA - (When would this be
the case? - ACA is Threshold Alt+200
for day for night its THR Alt+300? in a light twin)so its possible for this to occur on an ILS then I would start the GA at (not
before) ACA as well but its a difficult
and good question for an IR Instructor