Difference between 時に、時は、時には

Question

I am having a hard time figuring these out, it turns out that I get corrected by native speakers a lot, when I use one of them, they will correct me saying that another particle should be used instead.

大学に行く時に、もう夜なんだよ。

大学に行く時は、もう夜なんだよ。

大学に行く時には、もう夜なんだよ

At this point I am completly at lost in how different these should be, one guess would be that に should be when I wanna talk what happens in that "moment" and は when I wanna talk about that "moment" directly.

If my example is bad, please use a better one for exaplining the matter.

ps: The only related answer I found was this What is the difference between 時に and 時は but it didn't clear out much for me, honestly.

Answer 1

I'll show you the difference by some examples like:

1. 大学に行く時に、雨が降る。
2. 大学に行く時は、雨が降る。しかし、大学に行かない時は、雨が降らない。
3. （今は雨が降っていないが、）大学に行く時には、雨が降るでしょう。
   ３'.（今は雨が降っていないが、）大学に行く時には、雨が降るので、傘を持っていかなければならない。

The sentence example 1 is a normal expression, which means when I go to college, it rains.

は in the example 2 is a topic marker, and 大学に行く時 in the former sentence is contrasted, in this example, to 大学に行かない時 in the following sentence by the use of は instead of に. The whole meaning of the example 2 would be "In contrast to the other case, it rains when I go to college. But, it would not rain when I don't go there".

には in the example 3 is used to give the sentence a certain condition or situation; in this sentence the condition is the time when I depart to college. The meaning of the sentence example is that "As for the time, it will rain when I go to college, (though it's not raining now).

Answer 2

大学に行く時に もう夜なんだ is "it's when we go to our college that it has already been evening". It's because this sentence lacks topic parts, but nevertheless is an independent sentence (without hidden informations) of statement that expresses your assumption. So, it has to be interpreted as the so-called exhaustive listing が usage.

大学に行くときは and 大学に行くときには can be used similarly but usually, the former is more likely a plain main topic, as someone says, while the latter には version tends to convey a sense of concession, that is, "it will have already been evening when we go to our college, no matter how late".

Answer 3

大学に行く時に、もう夜だったんだよ。

Simply modifying the main part of the sentence by adding the information of the time.

大学に行く時は、もう夜だったんだよ。

The time is the main topic of the sentence.

大学に行く時には、もう夜だったんだよ

When you leave for the university is the main topic.

I guess in English and many other languages these constructions are same and use other things to make nuances and that is the problem that confuses many people.