Hi Anthony
The ESA legislation does not allow any extension of the time allowed to return the ESA50, the DWP can decide to accept a late return but there are no circumstances where they can change the return date that you have already received.
Have a look at our ESA/UC Claim guide on the following link and if you have any specific questions then come back to the forum.
www.benefitsandwork.co.uk/help-for-claimants/esa1 Gary