Is it permissible to take a sum of money that was mistakenly deposited into an account and consider it as compensation for unremunerated overtime hours, knowing that it is less than what is due and does not cause harm to the accountant?

If the company's work system stipulates your entitlement to overtime pay and you have not been compensated for it, then it is permissible for you to benefit from the amount that was incorrectly deposited into your account to secure this right, based on the principle of "Mas'alat al-Zafar" (the issue of gaining possession). A condition for this to be permissible is that it does not result in harm to anyone, such as the accountant. If there is harm to the accountant, then it is not permissible for you to take the amount.