I rarely completely change out the bedding, no matter what it is. I spot-clean every few days (probably should do so more often), and maybe every several months, if I decide the enclosure needs an overhaul, I'll change everything out.
I use coconut coir. I spot clean all the time. I have had my leopard for a year this past May. I totally changed it once, so far. Now he is outside during the day, so there isn't much to clean during the summer/warm days, mostly winters. Co nut coir keeps moisture very well for humidity and won't mold, if you keep up with the spot cleaning.
I've used coconut coir, but it kills earthworms and I kind of like to have those in the enclosure with the torts. I only do a complete change of bedding if I have a use for the old bedding in my garden. I've been using a blend of cypress mulch, coir, and organic potting soil.
My best answer to this is "as needed". There are many factors to consider. I soak babies daily and they usually poop in their soak water, so there is really no need for me to change the bedding. I just spot clean most of the time.