Method 1 (transaction value): time element
The WCO Technical Committee on Customs Valuation has considered whether there is a time constraint on a sale being valid for customs purposes (EN 1.1). It concluded that as long as the other conditions are met, there is no time constraint.
This means that if the contract of sale was concluded significantly before the goods were imported, the sale price is still an acceptable Method 1 transaction.
It does not matter if the price of the goods fluctuated subsequent to the sale but prior to the importation, as long as the full price paid or payable is declared.
None of the foregoing makes any difference to the material time for valuation, which is when the goods are entered into free circulation in the EC.