Use the past form. The only time a question of whether it's subjunctive or indicative arises is with the verb 'be' and their is no clear answer. Just as with the second conditional, some use 'was'and some 'were', so both are fine.
How would I know if a person is using the indicative or the subjunctive in "It's high time you WENT to bed / LEARNT your lesson" ? You wouldn't!