Lazybones
Hero
Based on how many 5-room dungeons I've run as one-shots, I could easily see each one of the Caves of Chaos taking up a game session. I know they're using milestone leveling, and while I don't know where the thresholds are, I wouldn't be surprised if the first level up came in the keep, the second after the wilderness, and then the third level is exploring the caves. Based on some of the names shown in the Caves book (in addition to the old "Kobold Cave" and "Goblin Cave" there was a "Mephit Cave" and a "Nothic Cave"), I suspect that the expectation is experienced characters exploring there.