Ok, so I think I’ve determined exactly when the second opening must take place:

[Steven gives Connie Rose’s Sword. But they hear Connie’s mom coming home.]

[Connie changes into a collared, sleeveless shirt, and grabs a book. She and Steven a run back to Beach City on foot for a quick BBQ party with Greg and the Crystal Gems. For the sake of appearance, Connie and Steven arrive separately.]

[Ignoring the fact that they’ve found Lion, and are at the Temple, Steven and Connie run back to Connie’s house with the sword. Connie changes back into the shirt she was wearing, and they disguise the sword as a coat rack.]

[Connie’s mom finds and takes the sword.]

[Connie never holds the sword while wearing her glasses again.]