must you obey an instruction within a certain timeframe or can you schedule all additional or changed work after completing your original scope?
Under 14.3 the Project Manager can instruct a change in the Works Information but no specific requirement on timing on implementation of that change is given. Turning to clause 61.1 There is a requirement on the Contractor to put the instruction (which has given rise to the compensation event) into effect, but again there is no mention on timing.
While there is no explicit requirement on timing the present tense approach of the NEC and the phrasing of the clauses means that the instruction should be complied with immediately, at least in the sense of following the procedure to incorporate the changed work into the project even if not actually carrying out the changed work.
HOWEVER, unless the instruction requires a particular sequence to be adopted it is for the contractor to decide the sequence of his works subject to the valuation of any compensation event being based on clause 63.7 which makes an assumption that the contractor reacts competently and promptly to any change and that time and Defined Cost are reasonably incurred. So, taking a very simple example, if a project is at a stage where foundations are complete and the Project Manager issues a change to those foundations that change must be acknowledged and implemented and the work carried out immediately. If at the same stage in construction the Project Manager made a change to the type of roof tiles the instruction must be acknowledged and incorporated into the programme for the works immediately but the work itself would obviously not happen until it was appropriate to carry out roofing activities.
As a final thought, when considering sequencing the contractor will also have to consider carefully the programing requirements and the possible reasons for rejection of an update under clause 31.3. If it is not practicable to carry out the work at the end it will need to be programed earlier in order to keep programmes being accepted.
In summary, there is no specific time limit for compliance but neither can you simply leave it all to the end. How and when you carry out the work depends on its type and nature BUT compliance in the sense of programing and dealing with the compensation event should begin immediately on receipt of the instruction.