Here “quand” doesn’t modify (well depends on what you mean by modifiy) “deux ou trois mois” it just means “when” so when the things happened he decided to do maybe something different we don’t know at this part of the sentence, but something happened.

You’re right for the second, here “fait” is a noun, it can be translate as “fact”. In is not too difficult to find this is a noun in your sentence because just before you have “un petit” and “petit” is an adjective, and you also know how much of “petit” there is, here “un”. So “fait” in your sentence cannot be a verb there.

If you look for what verb it comes from, this is “faire” which means “to do” or “to make” we use only one for the both verbs you have in English.

And the last one, depends too on what you mean by “refer to”. Here “que” means that because something happened (“quand un petit fait très bizarre”) then he chose to stay “je restai”.

Do you understand what I mean, do you need more precision ? I can translate the text with a basic English and you’ll be sure to have a correct translation.

Hope it can help, have a good day.

Ok tough one.

Quand can either be an interrogative pronoun or a conjunction. As a side note, the relative pronoun for a noun that denotes time is not quand but où. Here it’s necessarily a conjunction because there’s no question (neither direct nor indirect). When quand is used as a conjunction it can have two meanings. The more common one is to introduce a subordinate clause that defines when the main clause occurs. For example: Quand il pleut, je chante. But here it’s different. In a narration it sometimes introduces a sudden event. A longer equivalent version is quand tout à coup… (when suddenly).

Fait dans un petit fait très bizarre is a noun, meaning “a fact”. Suddenly, this quite insignificant but very odd fact led to ensuing consequences.

Que in the last clause might be confusing. It’s not a relative pronoun, so rester has no object. Rather it’s part of a “tel(le) … que” construction. Again, not the most standard one… It’s not a comparative (such as) but a correlative (such that). It’s the same construction as in, for example, “He was such a fool that he ignored it”. According to the text, what followed from that odd fact was such a “suite de découvertes” that he stayed.

Hopefully this elucidates the complex sentence.

(To be honest I had to read the sentence twice to understand this “tel, que” association. I deem it a little unnatural. So I’d be eager to know what was the original phrasing… for better or worse.)