Yeah, confusing isn't it. It really is a regional thing
Meals at set times in the day
Breakfast = first meal on waking
Lunch = always taken sometime in the middle(ish) of the day
Supper = usually mid evening or before bed
Tea = (apart from the drink
) early/later evening.
All the above are meals that are pretty much static. If you decided to have a breakfast type meal before bed, you would probably still call is supper.
Dinner/Tea. These are the confusing ones. Dinner is the main meal of the day. Could be taken at lunchtime or evening after work but it's still usually the main meal.
Tea. For me, tea is when you have buffet type foods..ie cakes, sandwiches etc, but for my husband, it's the evening meal whether it's sandwiches and cakes, or a full on hot meal. Go figure.
27 years of marriage and it still confuses me.