It takes Jelly around 2 hours to melt if the temperature is 100 F or more.
However at room temperature the Jelly should not melt at all because it's a solid such as Jelly that you put on sandwiches.
The Jelly in the jar will remain Jelly for a long time.
That is unless the heat in the room gets really hot.
I once left a jar of jelly out in my hot car and it was melted into a liquid after a day of being in the hot car.
However once the Jelly was put into the refrigerator the Jelly turned back into Jelly.
So under normal conditions the Jelly should not melt but Jelly can melt if it gets hot enough.
Also for Jello it can melt after setting within a couple hours if the temperature is warm enough as well.
If the room temperature gets to 80 F or above then the Jello could also melt in 2 to 4 hours.