AppleTalk node address allocation occurs when an ARA MP Server's ports are configured at startup. When a port is turned on, the ARA MP Server goes on the network to see what node addresses are available and allocates one per port based on that availability, in other words, dynamic address allocation. That is why configuring the ports takes some time.
A port will retain this same node address for all calls made to that port, even if someone dials in, disconnects, and then dials back to the same port. The same node address will be used. If the port is turned off, the node address may get used by another computer on the network. When you turn the port back on, the process mentioned above is repeated.
So, to answer the question, the node address is "static" as long as the port is on.