Here's a trimmed audio file. The first exchange appears to be KBUR Tower with an aircraft preparing for departure notifying them of the closure "for cleaning" and "at least two hours". The second item is the actual ATC Zero announcement from KBUR Tower. Interesting to hear that they note "VFR Traffic is not allowed during the ATCT closure." -- I couldn't find a NOTAM or TFR referring to that.
No other traffic in the 2300-2330Z archive was interesting enough to include in the clip. Also, as I listen to a live feed, they *JUST* re-opened the tower as of 0309Z.
My guess after the fact? Given the timing, etc, and the fact that KBUR appears to be manned 24/7, I'm guessing that someone caught COVID, and they were doing a disinfection run in the tower.