What time do you usually eat dinner?
I think it really depends on YOU and your circumstances when you dine. Meaning: do you have kids? what time do they need to eat? (for example, when my dd was a wee toddler, we would eat much much earlier since she went to bed so much earlier than she would now that she is 13)
Also, what time are you used to eating dinner? (ok, adjusted for any time zone changes!)
also, take into account when/what you are eating for breakfast and lunch. If you get up kind of late and eat a big breakfast, then you are hitting say, Crystal Palace (a buffet where it's easy to over-eat!) at 1pm, you probably wouldn't want to eat a big sit-down dinner again at 6pm. But then, maybe you would, if that's your habit. You have to go with your usual schedule and routines that already work for your family, I think.
For us, we don't eat much breakfast or lunch (never sit-down, TS places), we tend to eat a light meal at an early brunch-ish time, and (as I already mentioned) especially when dd was very young we would eat a big dinner early--like 6pm. Now that she is older, we eat a bit later. If it was just dh and I, we would probably eat a lot later, LOL.