What are the rules for the order of time adverbs?
You said:

&quot;However, structure 2. does not seem to apply for all adverbs of time,
in particular for some time adverbs indicating habitual actions such
as 经常 (often), 总是 (always) or 一般 (usually). &quot;

You probably mixed up time words with frequency words. Those are quotes from your links on &quot;ChineseGrammarWiki&quot;:

Remembering where to put the time words, such as &quot;yesterday,&quot;
&quot;tomorrow,&quot; &quot;this week,&quot; etc. in a sentence is really important in
order to speak Chinese correctly.
Time words can appear in one of two positions in the sentence in Chinese: either &gt; at the beginning of the sentence (before the subject), or directly after the
subject. The structures are:
Time + Subj. + Verb + Obj. 
Subj. + Time + Verb + Obj.
From Time words and word order


&quot;...常常 and 经常 both can be used to express frequency...&quot;
From Comparing changchang and jingchang

So, that answers Q1: 
&quot;Which adverbs of time can follow structure 2?&quot; 
In this case, the answer would be &quot;none&quot;, since the words mentioned in the Wiki that relate to time, are proper nouns (They are names identifying different parts of time), not adverbs.
Let's look at your sample sentences given in the &quot;examples&quot; section of &quot;Q2&quot;:

周末我经常去学校
我一般12点睡觉

When we remove the last section from the sentences for simplicity, then identify the role of each word, we get this:

&quot;周末我经常&quot;

&quot;周末&quot;: proper noun of time
&quot;我&quot;: proper noun of subject
&quot;经常&quot;: adverb of frequency


&quot;我一般12点&quot;

&quot;我&quot;: proper noun of subject
&quot;一般&quot;: adverb of frequency
&quot;12点&quot;: proper noun of time



Because those 2 formats are accepted, without changing the meaning of the sentence, and because frequency words cannot be located at the beginning of a sentence (As mentioned in Q1), therefore, the answer to Q2: 
&quot;When there are several adverbs of time, is there a rule indicating their order?&quot;
is &quot;Yes&quot;.

Hope this helps. If not, correct me.