Meaning of に in 早くに


These constructions both have Google hits: [もっと早く **に**
言う](https://www.google.com/search?q=%22%E3%82%82%E3%81%A3%E3%81%A8%E6%97%A9%E3%81%8F%E3%81%AB%E8%A8%80%E3%81%86%22)
and
[もっと早く言う](https://www.google.com/search?q=%22%E3%82%82%E3%81%A3%E3%81%A8%E6%97%A9%E3%81%8F%E8%A8%80%E3%81%86%22).

They seem to mean more or less the same thing. But what exactly does this に
mean and when can we use に after an adverb?

I don't think we can say stuff like *`強くに叩く` for just any adverb.

Maybe it adds some temporal nuance, like までに expressing a deadline? Is this
phenomenon limited to 早くに?




早く in 早く言う is (functioning as) an adverb (or, the adverbial form of the
i-adjective 早い.)  
早く in 早くに言う is a noun (the noun form of the i-adjective 早い --
形容詞「早い」の連用形「早く」が名詞になったもの). So 「早く+に」 is literally "at + an early time".

Similar examples of this noun form:

>   * 遅く -- こんな **遅く** に何の用だ
>   * 遠く -- **遠く** で雷が鳴っている
>   * 近く -- **近く** まで来た
>   * 深く -- 海の **深く** に沈む
>

Not all i-adjectives work like this (eg 美しく, 明るく, 大きく can not be a noun.) Only
several i-adjectives expressing the degree of time and space have this noun
form (eg 遅く, 早く, 近く, 遠く, 深く, 古く, 高く, 低く).




早く in 早く言う is (functioning as) an adverb (or, the adverbial form of the
i-adjective 早い.)  
早く in 早くに言う is a noun (the noun form of the i-adjective 早い --
形容詞「早い」の連用形「早く」が名詞になったもの). So 「早く+に」 is literally "at + an early time".

Similar examples of this noun form:

>   * 遅く -- こんな **遅く** に何の用だ
>   * 遠く -- **遠く** で雷が鳴っている
>   * 近く -- **近く** まで来た
>   * 深く -- 海の **深く** に沈む
>

Not all i-adjectives work like this (eg 美しく, 明るく, 大きく can not be a noun.) Only
several i-adjectives expressing the degree of time and space have this noun
form (eg 遅く, 早く, 近く, 遠く, 深く, 古く, 高く, 低く).

