Whose boots are you using? If they are Rx boots they can't be left on for more than a few hours. I think I read around four hours but I can't remember.
If they are from the EasyCare line of trail riding boots (and they have been properly fit to the horse), they can stay on for up to 12 hours daily, maxmum.
I kept Boas and Lily pads on my foundered horse, every day, from the second week of March to October 18th. No more than 12 hours however. Joker walked off in those boots like he'd gone to Heaven but, he was foundered pretty bad in both fronts.
Boas are a semi-agressive grip boot, so the grip also might make a difference to your horse.
EDITED TO ADD: Yes, ditto Loosie. I forgot -- wash the insides of the boots EVERY NIGHT with warm water and Dawn dish soap. Buy yourself a long-handled household scrub brush that is small enough to get inside the boots. If you wash them at night, they will be dry by morning for turnout.
I also picked and then brushed my horse's hooves every time I put those boots on. I applied Absorbine Hooflex Thrush Remedy around the whiteline and the frog/sulci area as a preventative. Bad as he was foundered, his whiteline miraculously stayed in tact and he never developed thrush. Eight months of that was brutal on me but it was worth it to see his hooves stay healthy.
He comes in every night to a stall with grid mats and shavings, which always gave his hooves a chance to air out and dry out in a healthy manner:)
Hope this helps