In Australia, we have lunch at lunch time [two words] (daytime), and tea at teatime [one word] (when it's dark), unless we go out, then it's dinner - you don't go to a restaurant to have tea, (unless it's just to the pub) - if in a restaurant, it's always dinner, [ ie, 'let's go out for dinner'] or if you have people over, they come for dinner (at night), not tea, although in summer, one usually invites friends over for a 'barbie' / 'bbq' rather than for tea or dinner, and that can be any time from about 11 am onwards!