[Gorest Gump]

But if you think about it would a 'suicide bomber' choose a time to crash a plane in a building when it was empty to avoid killing innocent people? I don't think so

If the 9/11 attacks had started 1 hour later, the death toll would have been much higher. So why didn't the terrorists plan for an attack later in the day? Perhaps it has something to do with opportunity. You don't just get in a plane and take off whenever you want. At least I don't think you can do that.

[Riflema]

According to one of the earlier posts - this building is "above" the railway station. So, it's after office hours (just) and people are headed to the trains - hey - let's bring down the building on the railway station!

[codebreaker]

The Pennslyvania plane was delayed 40 minutes on the runway, that was what gave them time to mount an attack.

[staytrue]

If the 9/11 attacks had started 1 hour later, the death toll would have been much higher

My guess is that they wanted an early morning flight because people are not that alert. Also, the planes needed to be 767 or 757 fully loaded with fuel for a transcontinental flight. Also, the early morning flights have few passengers which means an easier to control situation. I think less than 100 were on each plane.