Difference between 毎日に and 毎日

Question

When I saw that a fellow Japanese language student wrote: "僕は毎日に八時頃起きます。" According to Wiktionary 毎日 is already an adverb. I would personally say "僕は毎日八時頃起きます。"

Could you explain the difference between 毎日に and 毎日?

Answer 1

毎日 is never used with に. The same thing applies to 毎週、毎月、毎年、明日、昨日、今朝、今晩、今日、今、さっき、先週、来週、今週 etc.

In contrast, weekdays are with に (月曜日に、火曜日に etc.), and also when talking about time （５時に、３時半に etc.）.

I guess に is optional for 午前中 and 午後. I'd personally use 午前中 with に and 午後 without.