The right of an income beneficiary to income from property in trust arises at the time prescribed in the trust instrument, or, if no time is prescribed and the person receiving the right to income is the first income beneficiary to receive a right to income from the property, then:
(1) At the time the property becomes subject to the trust, with respect to property transferred by inter vivos disposition.
(2) At the time when, under the laws regulating donations mortis causa, the legatee of the same type of legacy free of trust is entitled to receive income from such a legacy, with respect to property transferred by testamentary disposition.