Im sure this was covered but color me a moron, I can't find it,

If Im traveling international from Asia - SFO and have a connecting PS flight the next morning to JFK, can I change that PS flight to a later flight as long as they have my fare bucket available, I had heard on some international trips this was not allowed which makes sense since the overnight stop in SFO is under 24 hours. If I originally ticketed it with the stop over 24 hours (what I want) the fare dif is almost $3000