Leaving conditioner on past the recommended time can actually cause the hair to go limp. With Motions CPR and other protein treatments, I try to stick to the amount of time specified.
i usually sit under the steamer for about 30 mins. when i use moisturizing conditioners like nexxus humectress and aveda brilliant conditoner i put a plastic bag over my head and leave it on for about 2 hours, if i have nowhere to go.