Promoters Frank Warren and Alex Krassyuk sat on the top table for around half an hour, patiently waiting for the fighters.
An energetic Dubois – wearing an understated tracksuit - eventually jogged on to the stage and saluted Warren.
Showman Usyk high-fived his team, bowed to around 50 or so members of the media and sang along to a Ukrainian song.
Dressed in a combat-like vest, he took his seat and began quietly reciting prayers while he clutched rosary beads.
Unsurprisingly, the conversation almost immediately turned to the punch from 21 months ago.
"As I sit here now, all day long that was an illegal blow. It's not about the belt line it's wear the navel is," Warren said.
Usyk continued to mouth his prayers and later put his head on the table in boredom. He was then involved in another war of words with Charles' son, heavyweight George Fox.
On Monday, Usyk suggested to Fox they should have a "street fight" with four members of their respective teams.
Fox, who was sitting at the back of the room a day later, said Usyk - a man who has defended his country against the Russian invasion - must have been rattled.