Keeping boiled potato warm
There are three things to consider. The first two are food safety.


Temperature: You say warm oven, but in order for food to be held for extended periods of time safely they need to be held at over 140° F. (source)
Time: Once you are no longer maintaining a safe temperature you have a short period of time before it is considered unsafe. Approximately 4 hours. This includes time it is sitting out for service.
Dried Boiled Potatoes: If you keep the potatoes in the oven they may dry out. although this is fairly preventable by covering and adding a touch extra moisture. This is also the least important of the three concerns as it doesn't constitute a danger.


I would recommend doing the boiling shortly before service. The actual cooking is not the hardest part of making boiled potatoes. The peeling and cutting is. Simply prep your potatoes in advance (even the day before) and store them in cold water to prevent them spoiling. Then rinse and boil just before. You shouldn't need more than 30 minutes to an hour for that quantity.

There is also another option (pointed out by GdD in comments), of preparing them in full and refrigerating them. Then it is a simple matter of reheating them just before serving. This may be your most ideal option because almost all of the work can be done before hand.