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Gillingham will have until mid-October to make permanent and loan transfers.
Domestic deals for contracted players can be made up until 5pm on Friday, October 16, 2020.
The standard window is open from Monday, July 27 and runs up until Monday, October 5, with an additional period for clubs to make “domestic only” deals.
During that extra 11-day period EFL clubs can transfer players between themselves and the Premier League, loan or permanent, but top-flight side will not be able to make deals with each other or sign players from abroad.
The EFL said: “The window for international registrations closes at 11pm on Monday 5 October, with an agreement in place with the Premier League for an extended two-week domestic only window which will close at 5pm on Friday 16 October."
Any new players signed are not allowed to play for their new clubs until the 2020/21 season, which is applicable to clubs involved in the EFL Championship play-offs.
The transfer window - which covers contracted players - is subject to approval from FIFA. League clubs can still sign free agents outside of those dates.
The 2020/21 season has no start date as yet but clubs have been voting on either August 29 or September 12.