Is the に time particle optional when talk about repeated action?


I have already learned about に time particle (in short: determines the action
time if the time expression isn't relative). But I saw some text where dropped
when used the まいとし, まいつき、まいにち etc.

For example:

> まいにち おちゃ を のんでいます。- I'm drinking tea every day.

Is this correct? Or should I use with the particle?:

> まいにち **に** おちゃ を のんでいます。- I'm drinking tea every day.

If the two sentence is correct then is the difference: the last sentence is
more formal than first?




Simply, まいとし, まいつき, まいにち and so on never take に. You have to remember which
word needs に and which word works on its own as an adverb. (In English, "every
month" and so on don't need "in" or "on", so this should not be surprising.)




Simply, まいとし, まいつき, まいにち and so on never take に. You have to remember which
word needs に and which word works on its own as an adverb. (In English, "every
month" and so on don't need "in" or "on", so this should not be surprising.)

