I would be cautious about leaving them folded for any lenght of time with out refolding. You can develop permanent creases in the quilt.
Do use pillow cases , so the quilt can breathe. If you must fold, take them out every few months and refold , being careful not to refold in the same place. I take mine out and layer them on a spare bed every few months for about a week, before putting them back.
At mimium a good reminder is when you change your clocks , its time to re-do ( refold , re- roll , rotate, etc) the quilts.