Is the thief sinful for delaying the return of stolen money to the heirs of the deceased?

Among the conditions for repentance from violations of people's rights is to restore them or seek absolution from the wronged party. Repentance is obligatory immediately, by scholarly consensus. Delaying the restoration of rights without a valid excuse is another sin that requires repentance. It is obligatory to hasten to restore rights immediately if the person is able to do so, whether these rights are borrowed items, usurped property, or possessions acquired through an invalid contract.