Explanation for 'noun + な + ので', is 'ので' still a 接続助詞 here?


I saw the following statement in a grammar book:

> 接続助詞 'ので' can only be placed after 用言 and 助動詞 in form of 連体形.

But in another text book it says that ので can also be placed after a noun, and
then the noun is concatenated with な, e.g. 時間なので.

Is 'noun + な + ので' a special case? Is role of 'ので' here different from being
placed after a verb/adj?

I searched similar questions:

  1. adj. + な [(noun) + な versus (verb) + な](https://japanese.stackexchange.com/questions/47998/noun-%e3%81%aa-versus-verb-%e3%81%aa)
  2. noun + な (but didn't cover whether in scope of 接続助詞) [What does "nanode" mean? What are its grammatical rules?](https://japanese.stackexchange.com/questions/19591/what-does-nanode-mean-what-are-its-grammatical-rules)

