| | Re: in/on/at Friday meeting?
It does seem weird. The "meeting" example is easy to analyse. If you say at the Friday meeting, then yes, you're talking about place. The noun here, and the most important element is meeting. That's what you're talking about, and "Friday" just modifies it, like an adjective - telling us which meeting we're talking about. Friday fills the same slot as eg next : I'll tell everyone at/in the Friday/next meeting. So the preposition must collocate with meeting, not with Friday , and therefore in or at are fine but not on. Think of it like this : if I said I'll tell everybody at the Friday/next meeting I could take Friday or next out of the sentence and it would still make sense - I'll tell everyone at the meeting. But I couldn't take out meeting :* I'll tell everyone at the Friday/next.
So why doesn't the same thing happen with Friday morning - why don't we say in the Friday morning? Here Friday is not an adjectival component describing morning - the two words form a single compound noun, of which Friday is seen as being the most important element. And therefore the preposition collocates with that.
I'm waffling a bit here as I don't have a grammar in front of me, but that seems a logical explanation. I'll check later and post again if I find anything that contradicts what I've said.