The lab has a system for announcing when it is open to the public. When set to open, anyone is welcome to turn up. You can open the space whenever you feel like hosting people.
This is a standard hackerspace pattern. Most spaces publish their state in SpaceAPI, which can be shown on maps, e.g. Hackerspaces Map
To open or close the lab, long press the green or red buttons on the plywood box beside the door in G1.