Not sure if bug or intended: In Abandoned Mine I start Ch3 with 10 days to roam. In Sunken Temple I get 12 days.
It's based on how many days you have left over from Ch2!
Whoa! In this case, it's amazing! I've always wondered how can I get all those prisoners in a few days I get, but if I can just rush lair ch2 and then have all this time in ch3 to explore - great!