Of course you are right an precisely, your statement is not different from mine.
IF THE CONTRACT states that the moment to complete is after the LFO and the snagging, you need to complete or, you will be consequently breaching the contract. At least, as you have said too, you find the builder has not complied and you notice that to him through a notharised letter.
But that is because of your contractual will, not becasue of the power of the License. So, a different thing can be agreed, and therefore when I intervene in the forum i prefer to not say a last word till I have seen what it has been agreed between the two parties in the contract.
With all my respect to your professional expertise and experience.
Maria de Castro