A spokesman for the Highways Agency said the closure on the A1 in North Yorkshire is now expected to remain in place until between 5.30pm and 6pm.
Earlier today they had anticipated that the road would re-open at around 3pm.
Police are continuing the search for the source of an explosion reported by staff at the Marne Barracks, in Catterick, at 3am.
More top news
"I would personally like to thank the local community for their amazing donations of food, toiletries and clothing. "
Owners John and Irene Hays say there is ''light at the end of the tunnel'', after the pandemic forced them to close 650 UK stores.
There has been resistance to calls to dismantle memorials to the explorer.