Why is it imperfect past tense instead of preterie

Hello! I have a spanish assignment, and i just don't know where to start. So my question is: Why is this sentence Imperfect? : El guardia dijo que no se podía entrar hasta las dos. We have an actual period, so what is the explanation? Please heeeelp! Thanks

The subject of the sentence is the guard. What he said was said in the past. The comment he made is an imperfect statement because it is incomplete and is imperfect. (In other words, he could still be saying it) If the sentence read " yesterday the gaurd said I could not enter until two" then it would be a definitive statement and complete therefore it would be preterite. I hope this helps.