It is a recommendation that the treatment should be done twice a year just before winter as this is the time with the change in weather that causes the product to dry out after the rainy season and will cause the product to contract. The wood is still “alive” and will need some moisture to give it life or nourishment. The product will also appear to be dull. Thus indicating and craving a treatment.
The other occasion will be just before the rainy season starts where the wood needs to be protected from excessive water caused by the rain and in some cases irrigation systems running close to the dwelling.