You can just make a func_door crush some nodes. However, enabling will be a bit tougher. As players always spawn in nodes closest to where they died (if node is ready to spawn), you could have LOTS of nodes (10-20, enough that max players can't queue all of them), in 2 places, 1 of those places is further from the map play area then the other. That way, every1 will spawn from the closer area and from there you teleport them to wherever. After that event, the first nodes would be crushed, and every1 will spawn in the 2nd area, from where you teleport them to somewhere else. With AMP you could make even more complex systems.