The discussion cites zakat, ṣadaqat al-fiṭr, ʿushr, unrestricted vows, and expiations as examples of duties not confined to a single short legal performance window.
Zakat has its own conditions of liability, including qualifying wealth.
Ṣadaqat al-fiṭr has a distinct cause of obligation and a separate question of payment.
Expiation depends upon the legally specified means and capacity.
An unrestricted vow does not fix a particular day in its formulation.
These obligations do not share every legal detail. Their common feature in this classification is the absence of the particular sort of time limit being discussed.