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1. What part of speech is "when" in this sentence?

- When he signs the contract doesn't matter.

2. Anything wrong with these two sentences?,

a- When he has signed the last book for the last fan, Dr. John Dr. John makes his way toward a limousine that will convey him to the other end of the fairgrounds.

b- When he has signed the contract doesn't matter.

If b is wrong, can we say that in noun clauses it is not correct to use "when" before "present perfect" but it is correct in adverbial clauses?
Comments  
. What part of speech is "when" in this sentence?

- When he signs the contract doesn't matter.

If I am not mistaken, the sentence should be “ It doesn’t matter when he signs the contract”. I believe “When” is an adverb.

im pretty sure that when isn't an adverb because most adverbs end in the suffix -ly
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Oh, and to back that up, adverbs are after the verb and technically "does" would be the verb. That's because doesn't is the contraction of does and not and does is a past tense verb
Actually, I remember now that "when," can be an adverb, noun, conjunction, or a pronoun.
I believe "When he signs, the contract doesn't matter" is correct while "When he has signed, the contract doesn't matter" is incorrect. The reason is because the whole thing has less to do with time but rather implies a general fact. Consequently, the tense in both clauses has to be the simple present I think. In my opinion, the part of speech for 'when' here is a relative adverb.
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when is acting as connecter in the above sentence (conjunction)
When is introducing the noun clause: When he signs the contract. That clause is the subject of the sentence. When itself is a subordinating conjunction, introducing the dependent clause.