We eat dinner at 4:30~5. DS takes forever to eat, but he just comes and goes till it's done. sitting there and doing it all in one go would drive us all mad. I'm not sure how we'd manage it if I was working as well and we had no choice but to start later....
If kids are hungry they will eat. If they don't eat dinner, it's most likely because they've actually eaten enough earlier in the day.
We used to do the cajoling, the encouraging, the bribing and offering alternatives to DS when he was younger and it became a nightmare.
They get supper if they've finished their dinner (ie, if they're actually still hungry). We no longer make any kind of deal about meals at all. This is it, you eat it. Don't want it? OK.