Lunch 12midday to 3pm. Dinner 6pm to 8pm. supper sometime after 9pm. Sometimes I eat all three, Fat cow! Teatime was in my younger days, somewhere it got replaced by Dinner. I don't know why. I prefer teatime, it sounds comforting
I call it "dinner". My other half calls it "tea". So we compromise at "supper".
At school there were dinner ladies who served hot food in the canteen. If you brought a packed lunch to school you ate it in the lunch room.
At home it was dinner at tea time.
At the weekends it was lunch in the middle of the day on Saturday and dinner in the middle of the day on a Sunday.
Supper was what you ate before bed.
My latest story - a short in the Gay Male category The Tutorial