Which time expressions take the に particle?

Question

The textbook Japanese for busy people 1 tells me, in lesson 6, that "relative time expressions like あした, らいしゅう, こんげつ and きょねん generally do not take any particles."
They exemplify this with sentences like:

スミスさんはあしたぎんこうにいきます。
チャンさんはきょねんにほんにきました。

One lesson later, they tell me that "unlike relative time expressions, specific time expressions take the particle に.

どようびに, 'on Saturday'
２００６ねんに, 'in 2006'"

They then provide these example sentences:

ジョンソンさんはらいしゅうのきんようびににほんにきます。
かいぎはすいようびです。

However, and contradicting the explanation given, the second example sentence does not take に. Furthermore, they do not provide any example as to why. Is there any rule that explains this? When do specific time expression take the に particle, and when don't they?

---

P.S.: I know no kanji, so please provide your answers in kana. Thank you.

Answer 1

About the question that isn't covered by the link Flaw provided:

However, and contradicting the explanation given, the second example sentence does not take に.

This is because here it is not an adverb nor a pronoun. Here です is a copula linking かいぎ to すいようび.

に would be correct when you have a different verb, as in

かいぎはすいようびにあります。