Thanks for all the plumbing vibes!
No new water leaks since last night, but the leaks seem to happen (at least, lately), between 6PM and 8PM.
The management sent someone to take a look today. At least wearing a mask. He was on a walkie-talkie with another guy in the apartments above us. They apparently cut out part of a wall upstairs, but didn't find a leak.
So, as DR Jrand70 says, we shall see what we shall see.