Where were Beatrice and Hero respectively during the balcony scene?

I actually don't recall this being explained in the text. If you find out, let me know

I've come up with a theory.

Hero’s whereabouts are unrevealed during the play. However, Borachio does mention that he suspects he will have to lure Hero away from her apartment for the plan. How he shall is unexplained. In Act II Scene 2 Borachio says he'll fashion some way to have Hero be away, but it's not specified how/for what. It's up to the individual production to justify it, but no explanation is given. "...for in the meantime I will so fashion the matter that Hero shall be absent; and there shall appear such seeming truth of Hero's disloyalty…” explains Borachio. Put simply, we do not know where she was, but the text provides the hint Borachio kept her occupied, perhaps by the fashion of trickery. It must have not had her wander around Messina looking for any individual or had her see any individual or she would have met them and whoever she accompanied spoken up during the wedding. Whatever she was told to do she had to do it alone, if Borachio did make up an excuse to get her to leave the house. Another theory states that Hero’s absence was not caused by Borachio’s trickery directly: He may have never come face to face with Hero after all. It is possible that Hero was gotten out of the house by Margaret. Margaret is a close friend to Hero, and she would easily have been able to sway Hero into leaving using this influence.

As for Beatrice:

Beatrice’s whereabouts continue to be unknown to anyone. Regarding the events of the day before the day before the wedding, however, it is entirely possible she sought alone time to think about her feelings regarding Benedick. She has realized her love for Benedick but continues to protest it. The thought of the failed relationship is in her mind. This is analyzed through her actions around Benedick up until when they confess their love. This is also analyzed by how she reacted to hearing the trap laid by Hero and Ursula in the garden. She might have snuck off to figure things out and meditate on her feelings. This would explain her absence the night before the wedding, as well as her lack of an alibi. She may have been uncomfortable explaining this.