Usually we heat RNA at 70 degree C for 1 min or 65 degree C for 5 min before gel loading into gel. I think, that's the threshold temperature for keeping your RNA safe. If you want to keep your RNA sample safe for long time, -80 degree C would be the best option. Best wishes.
Up to a maximum of 70 degree Celsius and i thick -80 degree Celsius is the optimum temperature to store for a longer time without compromising with the RIN value of RNA. Good luck.