Just wondering, when does one have to add the noch to the greetings? Does the noch implies that that part of the day (Tag, Abend) is about finishing?
I'd also would like to know whether it makes sense to add noch also to Morgen:
Guten/Schönen Morgen noch (?)
I've never heard it and it sounds perhaps strange, so if it's impossible, which is the reason?
It more or less implies that you're at the end of the conversation; you'd never start a conversation with: Einen Guten Tag noch.
So the actual use case would be (optionally before or after you said bye):
(Tschüss und) einen Guten Tag (dann) noch.
I've occasionally heard einen Guten Morgen noch, especially when you work on night shifts and say good bye to your fellow workers.
First of all: Guten/Schönen Morgen noch is not a greeting, it's a parting phrase. It's the noch that makes the difference.
The final noch just means something like for the rest of your day from here on. It can be quite an impression of some familiarity or intimacy to express your closeness with someone thorugh even your future thoughts for this person.
Most often it's just an empty phrase of everyday's obligingness... That said it then might be quite obvious that it also can mean the exact opposite when you say Guten Tag noch in an agressive or ironic voice. Maybe the Berlin bus driver treated you like a piece of clumsy baggage. When you get out at your station you might wish him a Schönen Tag noch emphasizing Schönen, meaning you wish him a bunch of football hooligans singing and dancing in his bus until the final station ;)
Be aware of regional differences of German language!
[any greeting] noch is used only in Germany. You never say "noch" after greetings in Austria (only german immigrants and german tourists do this).
btw: Never use schönen in greetings in Austria (Don't say schönen Tag, schönen Abend ... in Austria).
Read more about greetings in Austrian German here: Polite alternatives to "Grüß Gott"?
