I started studying Chinese only 3 months ago, so I can't speak how Chinese really works. But I do know that a language doesn't always need verb tenses. It just need to inform when something happened or will happen (and if it is completed or not and so on).
Even in English this kind of construction is possible:
"I'm going to Brazil."
and
"Next month I'm going to Brazil" (future meaning).
Similarly, it would be possible to say something like:
"Yesterday I finally finish the book"
Of course this is incorrect in English, but "yesterday" is enough to indicate that the event occurred in the past.