Define video start time in expression

I'm trying to make it so a video randomly plays back and forth using ease between a defined set of random time periods.

I have got this code I found and using and it works wonderfully, but It only works from the start of the video. I cannot tell it the starting frame or time to do it from.
After many hours of digging into expression help, trying to learn what I need I turned here for help.

Here is what I have so far:

start = 0;

end = 5;

seedRandom(index, true);

while (time > end) {

    rand = random(1, 9)

    start = end;

    end += rand;

}

maxVal = (end - start) / 2;

mid = (end + start) / 2;

if (time > mid)

  ease(time, mid + rand, end, maxVal, 0)

else

    ease(time, start, mid, 0, maxVal)