You will have to sleep with the product inside the trays. In order to have a satisfied result, 10 nights of Teeth Whitening treatment must be completed.
The product you have in hand is 22% peroxide. It’s a non-hazardous disinfectant for healthy teeth, but may burn the gum. When applied, drop a small among of gel per tooth so that the product will not overflow. If the product overflowed, simply sweep it up with a wet cotton swab.
You may experience some sensitivity after the fifth night. If too sensitive, stop for a few days and restart the treatment later on. If the whole treatment happens within a month, the result will be the same.