gee where in PA were they using a stop watch on a 55MPH road, they very unusual, They primarily use it on surface street in the 25 to 45 MPH. The biggest issue is what distance they measured you over. The shorter the distance the greater any error they can get.
I believe NJ assigns 2 points to your license for out of state tickets. So you have to decide whether it is worth fighting. If you search this forum there is plenty of information on how to fight a stopwatch ticket in PA