Does the 13 week period mentioned in clause 91.8 pertain to the period between the instructions being given to stop and restart or the dates for the works stopping and restarting?
Could you clarify what your contract Clause 91.8 actually says as this is not a standard clause under the NEC3 ECC form.
Apologies that should read 91.6 rather than 91.8.
The exact wording is as follows - If the Project Manager has instructed the Contractor to stop or not to start any substantial work or all work and an instruction allowing the work to re-start or start has not been given within thirteen weeks.
That looks like clause 91.6 in the standard form, so your contract may likely have been amended.
The 13 weeks period commences upon an instruction being given to stop or not to start, so the clock starts ticking upon the instruction being given. If a consequent instruction is not given 13 weeks later, or is given more than 13 weeks later, then the right to terminate applies.
Note that the party assuming this right is determined by the reason for the original instruction and that the right to terminate relates to ‘substantial work’, whatever that means, presumably based on the particular circumstances of your contract, or all work.