Dumb Sign On Door

As I walk by an Allstate office I noticed a sign on the door that reads, "Back in 15 minutes." What does that mean? Did they put up the sign 14 minutes ago in which case they'll be back in one minute? If I see the sign again 5 minutes later will it still be another 15 minutes until they return? What if their watch is broken? Does that mean they'll never be back?