Doesn't answer the in-universe question first asked, but the second origin for Speedy in 1955 (Adventure Comics #209) would probably be the latest I'd pick for silver-age swap for Green Arrow. Not sure on where earlier than that a transition point might be. Not sure, but it seems like they moved from an apartment to house at some point, too. I may try to see what I can find, though, just because. Will probably give up quickly, though. Of course, I have swap-to-bronze-age in mind for him, too, but everyone knows when that is, even if it doesn't have the distinctness of an earth-2 to earth-1 break.Now where the Super Friends and Green Arrow have their switching points is unknown. In fact, it may even be possible there is no set point but stories eventually going from one world to the other. Going through back issues and trying to identify stories as Earth-One or Earth-Two is far too lengthy and complicated a process for me to care about.
EDIT: Now that I think about it, that might be Roy's third origin. But I think it's second? I know first was the plane crash one where they took their identities at the same time. Then there's the scientist-father one, then the forest-ranger father one, but I can't recall what order they come in.
EDIT AGAIN: First it was the plane crash, then the scientist dad (very quickly forgotten), then the magnetized arrow in Adventure #262 in 1959. This being the case, I guess I can go with #246 or #256 with Ollie's new origin.