In case a Variation is initiated by the Engineer for prompt implementation .

... the Contractor may send a Notice to the Engineer, that the subject of the Variation was Unforeseeable (having regard to the scope and nature of the Works), hence, the Contractor is not to start implementing the varied work promptly.

... the Contractor is required to commence implementing the varied works and take records of all the details ( ... regarding the details of the varied works executed, expenditures incurred, and impact on progress etc.)

... the Contractor is required to commence implementing the varied works even if it would pose immediate hazard to the safety of public areas surrounding the Site

... the Contractor within 28 days after receiving such instruction shall submit to the Engineer a description of the varied work, a programme for its execution and a proposal for adjustment of the Contract Price.

... the Contractor is not bound to start implementing the varied works right up until the price for the varied works is fully agreed (or determined)