According to this post, Trump was physically at the rally and could have started the speech on time: https://greatawakening.win/p/11RhFbQ2gV/if-trump-knew-that-pence-would-b/
I would assume team Trump knew what antifa was going to do at the capitol building, so they left "on time" so Antifa thought the clock was ticking. Then they waited and MADE SURE the speech went long so the majority of Trump supporters WERE NOT there when they tried to breach the capitol building.
As I was watching the speech I kept wondering to myself why the hell he was still talking while the voting was starting. I eventually stopped watching the speech to watch the voting. I went on a drive to clear my head when I realized it was going to take all day. 20 minutes later I was back home and the capitol had been "overrun"...I thought to myself..."That was fast."
When I realized he wasn't coming on until 12, I wondered if it was sort of a call-back to the old Westerns like "High Noon".
From IMDB - > A town Marshal, despite the disagreements of his newlywed bride and the townspeople around him, must face a gang of deadly killers alone at high noon when the gang leader, an outlaw he sent up years ago, arrives on the noon train.