Mr Kwarteng said the new deadline would: "allow further information to be provided and assessed including any further consultation required".
Norfolk Vanguard and another wind farm planned by Vattenfall called Boreas are planned to make landfall at Happisburgh, with underground cables connecting it to a substation at Necton, near Swaffham, from where it will link into the National Grid.
Horsea Three would make landfall at Waybourne and link to a substation at Swardeston, south of Norwich.
Jenny Smedley, from the Necton Substations Action Group, said: "We're very pleased the secretary of state has given the project even more time, because that gives us more time to get our point across."
Mrs Smedley said a planning inspector and a representative from Vattenfall were in Necton last week to see the planned substation site, and she and other nearby residents were able to suggest an alternative.
She said: "The site they've chosen is the highest point in the area and it is on a farm that's very productive. But there's another farm quite close that's 10 metres lower, and the farmer is willing to sell it because they're already putting roads through his farm.
"The planning inspector was very interested in our alternative site."
Julian Pearson, from the parish council in nearby Holme Hale, said he did not object to the substation out of hand, but said its impact on the environment should be mitigated.
Mr Pearson, who has mocked up his own 'unofficial' graphic of what the substation would look like, based on measurements given, said: "They said they are not going to look at mitigation in detail until after consent is granted".
A spokesman for Ørsted said they welcomed the delay.
He said: "Ørsted requested a short extension to help conclude ongoing discussions with key stakeholders. We trust that these discussions should facilitate the secretary of state in making a positive determination on the project."
A spokesman from Vattenfall said: "We welcome confirmation of a decision timeline for Norfolk Vanguard. The projects can make a significant contribution to reaching 40GW by 2030, up from around 22GW today. Vattenfall continues to work with local and national stakeholders to deliver the best possible projects it can."