What is the legal period for washing the knuckles (barājim), by analogy with the specified period for shaving pubic hair (istihdād)?

Muslim narrated from Aisha that the Prophet, peace and blessings be upon him, said: "Ten are from the fitra (natural disposition)," and he mentioned among them "washing the barajim." The barajim refer to the knuckles and joints of the fingers, and washing them means cleaning the places where dirt accumulates. This also includes the dirt that gathers in the folds of the ear and the depths of the ear canal. There is no specific time limit for washing them.