Now, this is quite a situation which most of the students face at a time in their career. Everyone has got to give one exam or the other. Your case is special because while most of the students have some convergence with their competitive exam and boards syllabus, it is not so for you. NIFT syllabus is clearly different from the boards. So try to manage time wisely. You can go for an easy subject for optional maybe a vocational one which has more tilt towars practical aspect. For English, you can read it whenever you like in your free time. The main subject of yours need to be given proper time, so start be making a time table and proper strategy for the whole year and try to stick to it. Now this strategy can be different according to your need and sleep routine.
Good luck!