I am used to hearing "lunch" for the lunch period, and dinner for a big meal anytime after 4:00 or 5:00, usually 5:00 but at the buffets around here ( Utah ) they switch from lunch to dinner at 4:00 exactly and all day on  Sunday.

The other day a couple of girl friends called and said they would "do lunch", they said "we are doing lunch at..." 

"do lunch" is new to me, did you ever hear it?

I also noticed around here that older people sometimes say supper for the dinner meal, at night.