I am sure that the expression "zu Mittag" is the one to be used when talking about lunch. For example:
zu Mittag gehen wir ins Restaurant.
So far, so good. My 2 questions are:
Is zu Mittag limited only to the context of eating, or can it be applied to all other areas? In other words, can I use it as a Temporale Angabe for anything? Or for all other areas that do not include nutrition at around noon do I use "am Mittag"?
Why zu Mittag and not zum Mittag?