This tip is very important specially when very less time is left in your GATE exam. In this time, you should focus only on solving previous year GATE question papers instead of your GATE study material and PSU's question papers. These question papers (ISRO, DRDO, Coaching Material etc) might have very difficult and challenging problems, but the focus of the GATE exam is on your aptitude, rather than the depth of the subject. Therefore in my opinion, it's better to solve last 15 year GATE question papers multiple times rather than solving questions from other material.
If you really want a good rank in GATE, then you should utilize your last month in solving last 15 year papers at least twice. You can easily do this by solving at least one paper a day. I would suggest you that after getting up in the morning, first of all solve at least one GATE question paper. While solving the paper, keep in mind that you are sitting in the exam room. You can't refer any books, notes or solutions and you have just 3 hours time limit. After that you will be free to spent rest of the day in analyzing the question paper & your mistakes, revising notes and solving solving difficult problems etc.
I would also like to share my own experience which might help people who are working in some company. When I was preparing for my GATE Computer Science 2012 exam, in which I could achieve All India Rank 54, I used to get up between 4-5 am and then solve at least one question paper before going to office. Then in free time in office, I used to analyze the paper & my mistakes and discuss the difficult problems with my friend. Revising of the notes was used to be done by me mostly in evening. I hope it will help you in managing your preparation time with job.
P.S. If you liked this tip, then I would like to request you to like it and share it with your friends. If possible, you can also share your experience in the comment, which might help other people.