Yes, the latest time slot for intimates at the WP is 6pm. The time you choose depends on what time of year and what type of feel you are going for. Depending on the season, it might be dusk or darker at 6pm. I think that the beauty of the WP is enhanced when sunlight streams through the gorgeous windows. From the photos I have seen, you can't see the castle through the window at night. The windows just appear black. During the day, it is possible to take photos with the castle visible in the window. I guess you also have to consider whether you want a late lunch or dinner after your wedding. You may want to think about what restaurant you are interested in, and find out if they serve lunch and/or dinner. Good luck!