31 seconds!!
The full article I posted from the Merc quotes several engineers who say there was plenty of capacity left in the bridge and collapse was nowhere imminent. There was a much bigger risk of widespread panic and everybody trying to get off the bridge all at once.
What if a quake had happened!? Bet that extra load capacity would have vanished!
It was a bit ominous seeing the arch gone in real life. I knew something looked different; took a couple of seconds to figure it out.