Something like this, maybe:
Pos01 = [200,100,0];
Pos02 = [100,200,0];
Pos03 = [300,200,0];
moveTime = 0.3;
m = thisComp.marker;
n = 0;
if (m.numKeys > 0){
n = m.nearestKey(time).index;
if (m.key(n).time > time) n--;
}
if (n > 0){
t1 = m.key(n).time;
t2 = t1 + moveTime;
if (m.key(n).comment == "Pos01"){
ease(time,t1,t2,valueAtTime(t1),Pos01);
}else if(m.key(n).comment == "Pos02"){
ease(time,t1,t2,Pos01,Pos02);
}else if(m.key(n).comment == "Pos03"){
ease(time,t1,t2,Pos02,Pos03);
}else{
value;
}
}else{
value;
}