Depending on which Beaglexxxx distribution, and what things you have ripped out of them, they can take anywhere from 12 seconds to multiple minutes to boot.
So, either you need to create a very special custom uBoot to initialize your ESC's, or add a power switch, that is under user software control, that is not turned on until after the system has booted, and you can then initialize the ESC's within your alloted time, after turning on the power switch.
--- Graham
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