Does ongoing charity have a specific timeframe, ending when the asset upon which it was spent ceases to exist?

Perpetual charity (Sadaqah (definition) Jariyah) is an endowment (waqf) and similar acts whose benefit endures. The duration of the benefit varies depending on the endowed item. Some benefits are perpetual, like land, while others last for a period, like trees and buildings. However, an item that does not remain in a state from which benefit can be derived cannot be endowed. Endowing dirhams and dinars is possible by entrusting them to someone who invests them as a Mudarib (a partner in profit-sharing), with the profit being disbursed to the designated beneficiary. If one gives charity to purchase supplies such as heating devices, it is considered perpetual charity as long as those devices remain. However, if the charity is given to cover expenses like the Imam's salary, it is not perpetual, as its essence is consumed upon use.