Time expression : slow down, then stop

Hi everyone,

I've been looking for a solution for hours and I couldn't find any. Basically, I'm using this expression to make a layer rotate :

timeToStart = 4;

timeToStop = 14.60;

if ((time > timeToStart) && (time < timeToStop))

{

  time*400;

}

else

{

  value;

}

I would like the speed to decrease a little before the layer stops, so that the motion looks more natural. Does anybody know how I could do this?

Thanks a lot !