There is an idiomatic expression "it is time I verbed" (meaning "it is time to verb") which is fairly firmly established in modern English, but it seems to be due to a grammatically incorrect reinterpretation of an idiom. I don't believe there is any grammar justification for using the past tense here.
Look at this Ngram. While you can't deduce this directly from the Ngram, the first uses of "it is time I" all are followed either by the present ("it is time I proceed to ...") or by "should", with the majority of them followed by "should". The modal verb "should" can either express obligation, or be the past tense of "shall". In this construction, it originally expressed obligation, but people seem to have reinterpreted the usage "it is time I should" as a past tense, and started saying "it is time I verbed". During the 19th century, some people (most significantly Sir Walter Scott) reinterpreted it as a subjunctive; you can see this in the Ngram for "it is time I was/were"; this usage died out along with most other uses of the subjunctive. Today, Ngrams shows you that many people still use the present rather than the past in this construction.
EDIT: I'm not sure I completely believe my original answer any more. The original "It is time I should" might have been the subjunctive of "shall", where "shall" in this case indicated the future, rather than indicating an obligation. One can see that "should" was used for the future subjunctive by considering how often "ordered that he" was followed by "should". There's no obligation in orders.
See Ngrams. On the other hand, this also explains why people took "it is time I should" for a subjunctive, even if it wasn't.