You asked about conjunction sentences with "when" and "and" which can be divided by commas. "When" is not a conjunction word. Conjunctions are "and, but, for, yet" see: http://www.english-grammar-revolution.com/list-of-conjunctions.html You asked what grammatical function conjunctions perform. They combine two independent clauses (sentences) into one. For instance: The cat knocked over the flowers. The cat sat on my laptop. The cat knocked over the flowers and sat on my laptop. A comma is not necessary if the independent clauses are simple like what I used. Otherwise, technically it is required to use a comma before the conjunction word. http://www.grammar-monster.com/lessons/commas_before_conjunctions.htm In your examples: Eg. As it is, though, I can not deny that when April comes I find myself going out to learn on the fence and look at that miserable plot of land,... Your use of When in this sentence is fine, but it is not a conjunction. Note 1: "But" is a conjunction, which I just used in the previous sentence. Note 2: In the previous note I sectioned off part of the sentence with a comma and which. This is not a conjunction, it is a nonessential clause, which provides supplementary information. http://www.grammarbook.com/grammar/whoVwhVt.asp Eg. So I thought I would spend the night in Central Park , and, having stuffed my small rucksack with a sleeping bag, I arrived one heavy muggy Friday to do just that : Too many commas around and. This is a run on sentence with poor grammar. Do not consider it any more as an example to learn from. "At the same time", and "at that time" mean something else. It will help people to answer you if you keep your questions focused on one topic at a time.

Could you provide examples?