a week? two days? depends really on what level of sophistication and education this civilization has… they would, probably have knowledge and concept of this "open expanse" devoid of the canopy of stone and mountains, the empty barrier with strange stuff moving over it that serves as an inadequate ceiling… at least if they can exile people up there and if the people were even remotely curious about the borders of their world and what lay beyond… then it would vary depending upon what myths and superstition they attach to this "sky" (or whatever they would call the roof-of-nothing-but-confusing-object-moving-about-following-and-pestering-us-with-sudden-increases-and-decreases-in-temperature-and-suchness…).
