I haven’t tested this, but it should be close:
L1 = thisComp.layer("Line 1");
rect1 = L1.sourceRectAtTime(time,false);
x1 = L1.toComp([rect1.left+525,0])[0];
L2 = thisComp.layer("Line 2");
rect2 = L2.sourceRectAtTime(time,false);
x2 = L2.toComp([rect2.left+525,0])[0];
[Math.min(x1,x2), 540]