conditional tenses

please can anyone help me analyse the tenses in this conditional sentence:

"If we did not stay up so late, we would not be so tired."

What's the tense of "did not stay up" here? It's not past perfect, because that would be:

"If we had not stayed up so late, we would not be so tired."

The implication seems to be that we're in the habit of staying up late, both in the past and also the present. But there is also the 'hypothetical' implication that if we were not to stay up late (in the future), we would not be so tired.

Thanks for any help anyone can offer.