How long does the black bar usually remain. I thought it was 24 hours, but it feels like it was less than 12 this time. People were asking for it midday when I

How long does the black bar usually remain. I thought it was 24 hours, but it feels like it was less than 12 this time. People were asking for it midday when I checked HN and I didn't notice it until the evening. It is already gone in the early morning here.