A few weeks ago, I coined the word morfternoon, which refers to the period of time in a given day when it’s technically very late morning or even afternoon, but one is having such a slow start to one’s day that it’s effectively morning.
Sadly, I see that others have also coined this term; there are a few dozen instances of it on the web. Urban Dictionary’s top-ranked definition has to do with time zones, but its second definition is the same basic idea as mine: “Late morning but not quite afternoon. When you don’t know [whether] to say good morning or good afternoon.”
I hadn’t thought about the time-zone-greeting issue. It turns out that another option for greeting people in a different time zone is good maen, where maen is a (usually non-capitalized) acronym for “Morning, Afternoon, Evening, and Night.”