We arrived at BNE with much more than 10 min holding fuel. Our scheduled ETA was 19:30 and we weren't far off that time, but the captain announced that there wasn't a gate allocated/ready so we went into hold for what then developed into a long time - I didn't keep note of the time, but it seemed like 60 to 90 minutes. At one time the captain came back on and announced that there were major delays at BNE and we had been/were way back in a queue (some people said they heard a queue of 18 planes!). This was well before the on-airport incident had started. From news reports the incident started around 21:30, and I guess that when the incident happened we diverted to OOL for the first time - probably getting there around 22:00. At that stage we had been tooling around for probably 120 to 150 minutes. If BNE wasn't suffering delays in the first place we (SQ245) would have been on the ground about 90 minutes before the incident unfolded.
Before we even became aware of anything happening on the ground, at about 20:30 or 21:00, I speculated to my wife that there might be something going on at BNE (more than just not having a gate for us) seeing as we were holding so long. It was shortly after this that the captain said we had been in a queue of 18? planes.