I don’t know this so much, but try this:
> find the time in which the Opacity of the last Layer go to 100. Let’s suppose it is in 6:21, so…
o = thisComp.layer(thisLayer, -1).opacity.valueAtTime (time -.4); //value of opacity
oMax = 100; //maximum value
t = 6.7; //time when it gets to 100
if(time < t) o else oMax
I think there is an easier way like "when opacity gets to 100%, keep in until..." but I don't know exactly.
Lord Scales