Here are the three golden rules of getting the timing right on GMAT:
1) Know the time limit of each question e.g. you should only spend 1 minute on SC (Sentence Correction) questions and 2 mins on Quant questions. This understanding will help you spend the right amount of time on the right areas and topics.
2) Know the topics. The more you know and practice, the faster you will get at answering questions.
3) Know the tricks. For each topic there are tricks to do questions in a shorter way. It could be new formulas, plugging numbers or guessing. The right skill at the right time!
4) Guess your way out. If you have spent 4 mins on a 2 mins question, its time to guess and move on. You are probably spending time on a question that you will get wrong anyway.