the dinner hour varies from group to group --
we are barely home from work by 6:30 and would never eat before 7 -- we tended to try to get dinner on by 6:30 when our kids were young
6:30 seems like smack in the dinner hour to me except for people who do shift work and eat on a really different schedule
if one wants to have a cake and ice cream party for an adult (a bit weird in itself) then I think that 7 would be the absolute earliest -- and then make VERY clear that it is only dessert --
in all these discussions of times, one has to factor in travel time, clean up after dinner etc -- how many people eat dinner and have the dishes done and could then get ready and drive to someplace and be there at 6:30?