Yes, the Contractor can : that is what the dispute procedures are there for !
Do note that implied within clause 60.1 (8) is the ability for the Project Manager to change a decision previously communicated to the Contractor. However, the PM would presumably not change his or her mind unless the Contractor had presented a clear case for why he or she was wrong: I had one where the PM had not turned the page on the Contractor's programme thus giving him only 3 weeks extra rather than 17 weeks when you worked through the full logic.
Perhaps call an early warning meeting discuss.
Do note that implied within clause 60.1 (8) is the ability for the Project Manager to change a decision previously communicated to the Contractor. However, the PM would presumably not change his or her mind unless the Contractor had presented a clear case for why he or she was wrong: I had one where the PM had not turned the page on the Contractor's programme thus giving him only 3 weeks extra rather than 17 weeks when you worked through the full logic.
Perhaps call an early warning meeting discuss.