Trying to figure this out is almost like trying to pick the winning lottery number. This will sound crazy, but it really does depend on what kind of people are eating there that particular night. There aren't alot of perfect view patio tables and we've been there on some nights to see them all full before 7pm. Other times, a great table has opened up after 8pm.
You can't request a patio table when booking your PS and depending on how busy it is, they don't even allow you to wait for something to become available. You could try stopping by there during the afternoon and mentioning the special ocassion. It doesn't always work, but making note of it at a less busy time, might increase your chances.
If you're all adults and you don't mind nesting, I would try for a PS at 6:30ish. If you get lucky, just inform your waiter that you will be staying through Illuminations and tip accordingly. Take your time, enjoy the atmosphere (and the beer). The view is well worth the wait. If luck or weather is not on your side, you can still eat dinner in the restaurant and ask to be shown to the viewing area when it's time for Illuminations. It's standing room only, but still a nice view.
Tammi