When the Ancient Spirits of Evil speak to Mumm-Ra, he does not recognize their voices, though in both "The Doomgaze" and "Excalibur" he spoke with one of them so should have recognized at least two of the voices.
The Cave of Time is shown to age whoever enters it in spurts accompanied by a turquoise flash, but in its introduction in "Trouble with Time", it had a gradual, subtle effect on its victims.