Is Zakat immediately due on an amount of 12,0 Omani Riyals received from a cooperative society after four years, or must one wait for a hawl (full lunar year) to pass on the remaining amount at the end of the hawl?

You must pay zakat on the money you invested in the association, along with its profits, every year if it reaches the nisab, because the profit follows the principal. Delaying the payment of zakat is not permissible. You must now repent to Allah and pay the due zakat for the past four years, which includes the principal and its profits, knowing that the nisab is equivalent to 85 grams of gold.