If you are new to the school as well, then clearly you will need a certain amount of time just to establish yourself with your own class and get to know how the school works. However, you will quickly find that you are picking up all kinds of impressions and information about what is or is not going on. At some point, perhaps towards the middle of your first academic year, you will need to start gathering evidence in a more systematic way. If you are already established in the school but have this new responsibility you should be able to start your research immediately.