I don't think either time would make a difference in getting a patio table. It's just depends on how busy the R&C is. I think the 7:20 time will make your meal a little less rushed and you can always go out onto the patio when Illuminations starts. Good luck.
A party of 7 will more than likely get an upper patio table which is an obstructed view. You can view illuminations from the Rose and Crown viewing area no matter what table you have, even indoor tables. We eat at Rose and Crown every year and I have never seen a lower tier patio table with more than 4 people.