The deadline for expressing views on the proposed Stour Valley Visitor Centre in Horkesley Park near Nayland has been extended.
Developer Bunting and Sons’ wants to build a conservation and heritage centre off the A134 at Great Horkesley.
Proposals for the 117-acre site include a country park, art gallery, demonstration nursery and wildflower meadows as well as art studios.
Colchester Council planning officers, who have recommended approval, ordered reports from three consultants and, although one backed the scheme, they all raised concerns about its long-term viability.
People have until Tuesday to get their views into the council.
Will Pavry, chairman of the Stour Valley Action Group, has urged objectors to attend the planning committee meeting at Charter Hall, Colchester, on February 28 at 6pm to show the strength of opposition.