(a) A general or demonstrative testamentary gift usually bears interest at the legal rate after the expiration of 12 months from the death of the testator; provided, however, that when a general or demonstrative testamentary gift is to be paid at a later time or upon a later event, it bears no interest until such time or event.
(b) The general rule described in subsection (a) of this Code section yields to the equity and necessity of a particular case if the condition of the estate as to the payment of debts and testamentary gifts is doubtful or if the fund out of which the testamentary gift is to be paid is unavailable for all the charges made upon it or if any other equitable
circumstance intervenes.