Hi Mike,
the break comes after 90 (*) questions, and there's no specific time assigned for each of the two parts: you will have 4 hours overall. So indeed, whatever time you have left after replying the first 90 questions, you will be able to use it after the break, to complete the second part of the exam.
(*) Some say the break started after 89 questions. To be honest I can't remember if I replied to 89 or 90 questions. Anyway, as soon as you reply to the last question from the first part, you will be prompted to review all the questions from that part (possibly limiting to the marked ones) before submitting them and start the break. So there is no risk you submit the first part of the exam without being given the opportunity to review it.
Good luck on your exam!