OK - I've checked quite a few recipes & only found
one that said anything about time for cooking the potatoes. The rest just assume you know, although many tell you to peel & quarter them first. The main reason I don't is that Gram said it was a waste of time since they peel so much easier after cooking.

I'm still thinking it must be about 15 - 20 minutes because of the egg. (I hard boil my Easter eggs by bringing them to a boil, burning them to Low, cover & cook for 20 min. So cooking at a boil for 15 is probably enough.)
I forgot to mention earlier that my mother always made hers with minced onion. I don't because onions make me break out in hives. I think she used both celery salt & celery seeds in it too. Then at times she would also throw in some green pickle relish or chopped gerkins. She also always put in chopped parsley, but I never cared for it since it wasn't all the "chopped"...as a kid I hated the taste of anything
green 
and sprinkled with paprika before serving.
Oh - and for the vinegar...years ago I only used cider vinegar. Now I don't even have it in the house. LOL I use red wine vinegar for everything that doesn't get balsamic or rice vinegar.
While checking for cooking times I found one recipe that looks about right if you want help with measurements.
PA Dutch Potato Salad
* 1 cup mayonnaise
* 1 T. prepared yellow mustard
* 2 T. apple cider vinegar
* 2 T. sugar
* 1/4 tsp. celery seed
* 1 tsp. salt
* 1/4 tsp. pepper
* 6 medium potatoes - peeled, cooked, and diced
* 1/2 cup - chopped celery
* 1/2 cup chopped onion
* 3 hard boiled eggs - chopped
* 1/4 tsp. paprika
In a small bowl, whisk together the mayonnaise, mustard, vinegar, sugar, celery seed, salt and pepper. Set aside. In a large bowl, stir the diced potatoes, chopped celery , onion and hard boiled eggs together. Add the mayonnaise mixture to the vegetable mixture. Gently stir all the ingredients together. Refrigerate for at for least 1 hour before serving. Sprinkle with the paprika just before serving.