What time is dinner? Like Nelle, we've found we have to feed DS early to get him to eat. He just can't manage it once he's tired. And he'll wake up wanting food in the night too if he hasn't eaten properly.
So we do dinner early and always try to fill up as much as possible during the day - it's bad if I'm out and DH is in charge because he forgets about morning and afternoon tea and does lunch too late! Anyway, dinner is 4:30-5 and we also do supper just before bed to fill up a bit more if need be (just a small snack).

*sometimes* if dinner is just not going down at all I'll offer a sandwich instead.

I don't think there are hard and fast rules either, just a matter of figuring out what's going to work.