いつからか、翡翠がやってくれば平穏な朝を迎えられるような、そんな日課が出来上がっている。
Why is ような used before the comma?
I think it means:
Since who knows when, if Hisui comes, as if i am brought with a tranquil morning, that way the day starts.
But i do not understand why is ような used before the comma.
There certainly is a noun following 「～～ような」, if the noun does not directly follow it. That noun is 「[日課]{にっか}」.
「いつからか、[翡翠]{ひすい}がやってくれば[平穏]{へいおん}な[朝]{あさ}を[迎]{むか}えられるような、そんな日課が[出来上]{できあ}がっている。」
「翡翠がやってくれば平穏な朝を迎えられるような」 is an adjectival phrase that modifies 「日課」.
「そんな」 also modifies 「日課」.
「そんな」 here means "that sort of". The author could have just said 「翡翠がやってくれば平穏な朝を迎えられるような日課」 without using 「、そんな」.
「翡翠がやってくれば平穏な朝を迎えられるような」, however, is such a long and eloquent adjectival phrase that it could sound a little "affected" if the author placed 「日課」 directly following it.
By placing 「、そんな」(= "that sort of"), it could serve as a softener that brings the eloquence level down a bit.
My shot at a TL:
"Since who knows when, a sort of a daily routine has been formed in which I feel as if I could greet the dawn peacefully whenever Hisui comes/is here."
I'm a native speaker and I'm still not actually not sure… ☺
Although, Japanese sentences sometimes have the verb after the noun, although that might be a bit of a stretch. I believe if a predicate has a "、" or "を" after it, it is forming a compound sentence. I am still not sure… But I think it's a sentence structure quirk.
Hope I was able to help.
