Answer will depend on pest. Spiders, rodents, 3 months. Ants: only to largely reduce numbers initially. Termites 12 months after a full treatment, if there was some fault in our application or treatment.
Yes, we spray for Bindi, and the best time for that is from mid June to September before flowering commences.
You can’t buy it a Bunnings; I am not sure about the answer to that question as the company buys it direct from the wholesaler.
The spray we use is water based and does not leave a stain on carpets.
Insurance policies do not cover pest control as part of their standard or optional policies. You would have to have a policy especially written to cover pests such as termites which I imagine would be very expensive.