"It is quarter past eight."
Translation:Il est huit heures et quart.
How do you know now? If someone tells you the time in English they don't say "It is quarter past eight pm". You know it is pm.
If you are on the phone on the other side of the world and you ask what time it is where they are they might say "Il est huit heures et quart du soir".
I did answer it in the post I referred to:
The French only use the impersonal "Il est ..." when speaking of the time.
C'est is NEVER used when speaking of the time - that is a set in stone rule.
To understand c'est vs il est in general read the tips and notes here:
"C'est mercredi?"- "It is on Wednesday"...
We are speaking of time there -Wednesday- and we are using "C'est..."
I guess I am confused as well.
Btw: I tried opening the link you posted but it is not working on Android platform. Could you please report that if you can? Merci beaucoup!