Yeah you should place them earlier. 30 nights starts at the beginning of the blackout. Free Seattle takes place well before then. I don't have cutting black in front of me, but it should have the dates for these.
My advice is to not get pinned down by dates. Make things happen when it's good for the story.
It's good if 30 Nights happens in the cold months, because that adds a nice survival element to the story. The plot of 30 nights barely ever touches on it though.
Just one of the many ways 30 Nights is not a good book.