The phrase "day guarantee" means that something will be definitely done or fixed within a specified number of days, or you will get your money back or receive some other form of compensation. Full definition
We offer a 30 day guarantee on all of our full sized products. (truebotanicals.com)
The manufacturer backs this product with a solid 90 - day guarantee for replacement / repair of defective parts. (tinyfry.com)
The guaranteed policy has a thirty - day guarantee period in case you do not like it and the benefits stated do not decrease after the first two years. (secureseniorlifeinsurance.com)