Hi eloisegrace,
The Graphs and Relations module has more overlap with Methods than the Matrices module. However, the most challenging topic in Graphs (Linear Programming) has concepts that are not covered in Methods. So if you want to take the Graphs module, you will need to focus on Linear Programming - make sure you learn it really well and master the more difficult aspects of it.
However, you are probably aware that there is significant overlap between the Matrices and Networks modules. If your class teacher is teaching the Matrices module, it may be easier for you to learn these two modules really well.
Then you can use your reading time to decide which module to answer on each exam. Particularly in Exam 1, where you might find a really challenging question on one module, but feel more confident about the last few questions in another module.
Good luck!