I made a flow chart of which Mastodon posts end up in which timelines!
So, you can see how each instance will have a different local timeline, and even a slightly different federated timeline - and you can see why the federated timeline moves so much faster than the local one, too.
@a_breakin_glass Ohh, what's your objection to that?
I feel like tenuously-connected toots sneaking into the federated timelines and being seen by people who might otherwise not see them might be good? And if the toot is getting replied to it is probably not the Worst Toot Ever... But I don't really know, there might be reasons I've not yet considered!