(1) A lease instrument becomes liable to duty on the day of first execution.
(2) A lease instrument also becomes liable to duty on the making of a variation to the lease that increases the cost of the lease and where such a variation is made duty is chargeable on the amount of additional cost resulting from the variation.
(3) Duty shall be paid to the Commissioner within 90 days after the lease instrument becomes liable to duty, except as otherwise provided by this Chapter.