I need grammatical checks here!

Try to be more consistent with your tenses.

Sometimes, the statement was asked even before the class was finished. Without a doubt, no one asked a question because we knew asking questions shortens (tense) our break time. Whenever this things happens, I blamed the teacher's incompetent who couldn't complete her class on time. But now that the time has come to plan my own, imaginary classes, I realized how difficult planning classes is in terms of time.