Installing Airport Express Base Station to an Existing Wireless Network

I need to install an airport express base station to an existing wireless network. I work part time at a school where the network is being accessed alot. Since I am only part time, I don't have an opportunity to come in while the network is not being accessed. So is it okay if I install the new express station to the network while people are accessing it?

Sure, I don't think you need to restart the main airport base station to add another node, just the node you're adding has to be restarted to accept the new setting...