Spanish language Q&A Forum

Hello, in one of the lessons I read Tal Vez accepts both indicative and subjunctive, but when I included the indicative in my answer to the following question, it was marked wrong.

 Tal vez ________ una gala benéfica para los niños pobres. 

Could you please explain?

While I understand the explanation via timeframes and don't want to complicate things unnecessarily, this made me think:

Can't I use the imperfect (progressive) with such timeframes, too?

Ayer estaba limpiando la casa. (Should be ok.)
Ayer entre la 1 y las 2 estaba limpiando la casa. (?)
Ayer entre la 1 y las 2 estaba limpiando la casa cuando algo me asustó. (Should be ok.)

That is, can't the imperfect (progressive) be used with an explicit timeframe, too, as long as its function is descriptive or establishing a background, i.e. as long as the aspectual semantics are imperfective within the timeframe?