That's kind of right!
You use the subjunctive when it's following the "talvez" to express a future condition. If the "talvez" is at the end of the sentence, it doesn't matter what tense or idea you're trying to express:
Talvez eu precise pensar = Maybe I will need to think
Preciso/Precisarei pensar, talvez = I will need to think, maybe (it's common to use the Present tense to express future actions like this)