The first step to determine this is to take one mock exam from your study materials and see how far you get in 150 minutes. If you aren't fast enough, look for ways to go faster. For example suppose you see an a try statement without catch or finally. you don't even need to think about the rest of the code - just answer that it doesn't compile and move on.
It is enough if you have practiced on mock exams well. Knowing the concepts is one thing and recalling them to answer questions is another.
Also, don't make any question an ego issue We have had a few guys in our training course who ran out of time because they "had to" answer a particular question. Lost several valuable minutes and failed the exam.
Maor Pau wrote:150 minutes is enough for 70 questions?
If you know all required exam topics and concepts very well and you have practiced with some mock exams, you won't run out of time on the actual exam. And you even might have some time left to review a few questions.
Using the search function of this forum, you'll find several topics with several tips and tricks to efficiently manage your time on the exam (and what you can do if your running out of time):