What is the maximum time that Delta can hold on to checked luggage between flights?

I'm planning my (elderly) parents' itinerary, and Delta.com is giving options for 12~15h connecting time in SEA (ICN-SEA-PSC). Would the bags need to be taken out of the airport, or can they be dropped off at the connecting flight baggage drop in SEA, even with that many hours connecting time? I figured that they can possibly rest at a hotel in that amount of time, rather than be rushed with a two hour connecting time. But if they have to lug bags around, perhaps the 2 hour connection might be better.