We visit from Oklahoma and really want more time too. We went this past May for 8 days, so we just upgraded to a season pass and we're going to take an extra trip this Spring to take advantage of them.

I got the 4 days with the 5th day free. I was worried about when I'd need to upgrade, but I called and I was told it just needed to be before the ticket booths closed on the last day of the ticket.
The last day was my birthday and a blocked day, so I wanted to use the paper tickets for that day. The park closed that night at 11 or 12, but the booth was open until 1a.m. I think I got there about 11ish and it took 45 minutes to convert the tickets (with no wait), so be prepared for that.