I can't imagine you'd need very many days of traffic to narrow it down to a very small group of people though. If a device is coming into and out of the campus, that should be fairly easy to reconcile with visitor records. Given that this is one of the most secure locations in the world, I'm reasonably sure a comprehensive list of "who is and isn't on campus" at any given time is available.
My prosumer ubiquiti gear will give me the MAC address and AP that the device is connected to, along with signal strength. WiFiman and a 5 minute walk will give me the mapping of where had that signal strength from that AP and at that point I could find the device with a physical search. There is no way that this device can’t be found in a few hours by anyone who is even vaguely paying attention.