If your episodes are all set as day 0 content, iTunes will show them as all having the same date. iTunes sorts content by date first, and then alphanumerically per date.
Nanacast automatically offsets the time for each day 0 episode content by a slight difference (i.e. microseconds) in the date/time stamp for the <pubDate> of the episodes, which allows them to be sorted in iTunes with the same order you've sorted them in Nanacast (you can change the sorting order of episodes using the up (^) and down (v) arrows).
The sorting order applies across chapters if you have multiple Day 0 content organized across multiple chapters-- an episode at the top of chapter 2 will be time-stamped a few microseconds after an episode at the bottom of chapter 1, for example.
Note: Previously, in order to control the listing order in iTunes with day 0 episode content, it required structuring the title of your episodes alphanumerically in order to have them appear in an order that you prefer (such as starting the title with a date or number.) This is no longer required.
Additional keywords: Podcast, sorting