Control Layer in point of expression % Number Count

I have an expression that Dan  Ebberts created for number counting with a percentage sign

beginCount = 0;
stopCount = 100;

beginTime = 0; // start counting at time = 0
countDur = 4; // count for 4 seconds

"" + Math.round(linear(time,beginTime,beginTime + countDur,beginCount,stopCount)) + "%"

For my animation the layer starts around 16 seconds into my timeline and the expression has already finished before then.  Is there a way to control the
in point for a layer for this expression?

Thanks very much

Ira