Well from what I've observed, it appears to me Soros may have called it first. Then various other people reinforced the message in their own ways and others made adjustments to their plans and schedules to logistically help with moving the assets in or out of the way so the chances of success could be increased.

I would suggest that an assassination plot like this was war-gamed years ago so that players understood what their part of the overall script would be (even the patsy appears to have been setup for his role over the past few years). So the word to deploy was given when Trump announced an event within a favorable area of the country, and when they recognized through internal polling that Joe Biden had no chance of pulling off a believable steal this time (much less actually winning).

Everyone involved in the plot likely has some dark skeletons that will come out if Trump is elected for a third time. Thus the motivation is very high for each player to succeed at all costs.