Check with the manufacturer. Many pesticide-type products have an 800 number so you can call with questions.

Keeping the product cool but not cold at all times and well sealed will of course extend viability.

I only use Ultrafine Horticultural Oil. I have been using from the same 2 and a half gallon container for over 10 years without noticing any change in the product. It is paraffin based. Al