Adam had progressed massively and would spend around half the day in the dungeon each day, which would equate to an entire day within the dungeon.
His master found how much Adam slept unusual, but he realised that it seemed to be increasing his strength and he had assumed that Adam had some sort of cultivation method that would allow him to cultivate in his sleep.
Floor 3 had a desert-like environment, that was very hot and dry and was probably the hardest environment that Adam had to fight in up until that point, on par with Floor 1 that was a very cold environment.
With the Ethereal Reocery Skill he could more or less recover his body to a peak state, but that didn't mean he didn't feel pain, thirst and hunger while he was in his Dungeon Form, and it was still very hard to deal with.