We eat at Rose and Crown on almost every trip and I still find it hard to estimate a good ADR time to catch Illuminations. It just depends on the crowds, the servers and how much you order. Generally I try to aim for an hour to ninety minutes before Illuminations, but sometimes this is too late; occasionally I have gotten seated right away and am finished eating well before it is time. I have heard some people show up a good three or more hours and just sit at the table. I don't think this is fair to the restaurant to tie up a table that long.
We have had some gorgeous evenings in December, but I do remember one year we had a CP package, and all they could give us was an "outside" table, even though it must have been in the low 40s. That night everyone wanted an inside table, and with the CP package you are prepaid so you can't make a last minute cancellation! The terrace was enclosed with canvas walls, and they had heat lamps, but we were in a corner with a cold draft (wind, actually) coming in. We ate with hats, mufflers, coats and gloves on. At the time I was irritated, but now I look back and it was one of our family's great "remember when. . ." times!