Not quite sure if you need such a complex expression. Something as simple as this would work on the opacity.
time < inPoint;
If you are wanting to change the value with ease without constantly having to go into the expression and change the start time or move the layers inPoint. I use a text layer because I need to change the value all the time and have this set up.
s = parseInt(thisComp.layer("Amount").text.sourceText);
if (isNaN(s)) s = 0;
t = s + 1;