Accelerating an object for a brief time then back to normal speed

So I basically want to have an object at a set speed which at a press of a button will have a smooth acceleration boost for 2sec then drop back down to its normal speed

I've tried a simple way which basically changes the speed by a multiple then returning it back to its original speed but that messes with the lerp function I use to have a smooth travel by jerking the object backwards to a earlier position.

 journeyLength = Vector3.Distance(startPoint, endPoint);
 
 if(acceleration){
     var    distCovered = (Time.time - startTime) * speed * 2;
 }
 else{
     var    distCovered = (Time.time - startTime) * speed;
 }
 
 var fracJourney = distCovered / journeyLength;
         
 transform.position = Vector3.Lerp(startPoint, endPoint, fracJourney);