The extension will allow for advert breaks, meaning episodes will not be reduced following the show’s move from BBC One.
The popular baking show is expected to return to screens later this year with the new line-up.
Former presenters Mel Giedroyc and Sue Perkins have been succeeded by Noel Fielding and Sandi Toksvig.
The decision by Love Productions, the production company behind the cookery show, to switch to a rival broadcaster caused uproar last year, with the new line-up announcement sending Twitter into meltdown a few months later.
Fans criticised the new look quartet as a “parody” of the departing team
Fifteen To One and QI host Toksvig said she is honoured to be part of “this national treasure of a show”.
She added: “Noel Fielding is one of the nicest guys in show business.
“The first time I met him I felt like I had met a rather wayward cousin whose take on the world made me laugh.
“The only down side is that he has much better dress sense that I do ."
Former The Mighty Boosh star Fielding said: “GBBO is one of my favourite shows.
“I've always loved brightly coloured cakes and Sandi Toksvig so this is a dream come true for me! It's basically the double.”