Selecting posts before ‘x’ Date/Time

Sorry, this is n00b question, but I don’t seem to be able to find the answer anywhere. I’m using the Mimbo theme, which works great. But it shows excepts of posts in three separate areas on the front page, each from different category.

I want to populate these areas with posts all from the same category. E.g., the ‘lead story’ is the most recent post, the three ‘features’ are the next 3 most recent posts, and the ‘news posts’ are the next most recent after that.

The problem is that I can’t figure out how to get the date/time of each post, and then pass it as a parameter in the query_posts() function.