The best time to buy a visitor health insurance for your parents is when the entire trip has been planned out and the visa papers are all in order. This is critical because it often happens that one buys insurance plans and later because of some visa problems, the trip gets canceled or postponed. This becomes an unnecessary financial burden on you air travel deal because once an insurance policy is purchased and later you want to withdraw from it, there will be only a few companies who will refund you money. They may also deduct some fees and may demand a notice for the refund. Other companies may also decline your request for refund upfront.