When is zakat due on orphans' money held in bank accounts that cannot be withdrawn except with a court order? Is it permissible to pay it in installments, and what is its nisab and method of calculation?

Zakat is obligatory on a minor's wealth once they reach puberty, and their guardian must pay it on their behalf. As for an adult, they are obligated to make the intention for Zakat themselves. If the wealth is under the guardianship of the حسبى council (guardianship council) and cannot be utilized until a certain age, Zakat is not obligatory until the wealth is received and utilized, because a condition for Zakat is complete ownership. This is what is known as 'mal al-dimar' (unproductive or inaccessible wealth), and it is subject to Zakat for one year when it is taken possession of.