What is the permissible duration for utilizing a deposit (Wadi'ah), and how should it be disposed of?

A deposit is a trust, and it is not permissible for the one holding the deposit to benefit from it unless it is money and the holder is wealthy and has witnesses to it. In this case, it is permissible for him to dispose of it by returning its equivalent. If the owner of the deposit or his heirs are unknown, it should be given in charity for the benefit of Muslims. The correct thing to do is to give it in charity instead of keeping it without benefit.