That still leaves plenty of time for them to talk before the next day. If someone suddenly shows up and endangers the massive web of lies you’ve been feeding your nephew all these years, you get them out of the picture as soon as possible. Dead droids tell no tales.
Not that I believe Lucas intended back in the '70’s that the droids had ever been to Tatooine before in the first place. 😉
“Massive web of lies”.
Part of that web is tangled by the fact that as of 1977, Vader and Anakin were different people. (as in, the story was always in flux).
And i’m not saying Lucas intended it in 1977. I’m saying it fits a bit better (while still not being airtight) than people think.
Owen doesn’t remember 3-PO until Luke says that 3-PO mentioned Obi-Wan. At that point Owen tells Luke to have its memory wiped.
That brings it down to “minor contrivance” level at the very worst.