From watching those state of charge videos, the adapters are only a bit more than a foot so not much more from the 20' mentioned above.There are two plugs. Twenty feet (12 feet suggested usable) from charger to J1772, not specified to NEMA 14-50P. The pdf at this link may help:
This brings up another question for me. It is better to buy an NEMA 14-50 extension cord or a J1772 extension cord?