Not 100% sure I fully understand the question. The Contractor identifies the working areas in CD part 2. The working areas are the Site and those areas identified by the Contractor which are necessary to Providing the Works.
Clause 15.1 the Contractor may submit a proposal for adding to the Working Areas.
Are we in fact in this instance referring to The Site and boundaries of the site?
The access dates are stated in CD part 1 and are not in the gift of the PM to change. Clause 14.3 the PM can give an instruction to the Contractors which changes the Works Information or a Key date. Only the Parties to the contract clause 12.3 can change the access dates.
The fact that the Contractor is also not ready wouold seem to infer to me that the Parties should consider a Deed of Variation or Supplemental Agreement?