(a) "Purchaser" includes a person who purchases or acquires by exchange or contracts to purchase or acquire by exchange the same premises or any portion thereof or estate or interest therein, or acquires by assignment the rent to accrue from tenancies or subtenancies thereof in existence at the time of the assignment.

(b) Contract for sale includes an option to purchase or lease.

(c) A lease, or a contract or option, is recorded when a memorandum thereof is recorded as provided in section two hundred ninety-one-c or section two hundred ninety-four of this chapter.

(d) The recording of a contract or option, or memorandum thereof, pursuant to section two hundred ninety-four of this chapter, is effective up to and including the thirtieth day after the day fixed therein for the conveyance of title, or the thirtieth day after the last day fixed therein for the exercise of the option, provided, that if a written declaration of the exercise of the option has been recorded as provided in subdivision seven of section two hundred ninety-four, the recording of the option is effective to and including the thirtieth day after the last day fixed pursuant to the option agreement for the conveyance of title or the execution and delivery of the lease, as the case may be. An agreement extending the time for the conveyance of title, acknowledged or proved, and certified, in the manner to entitle a conveyance to be recorded, may be recorded, and the recording shall be effective up to and including the thirtieth day after the day fixed by such agreement for the conveyance of title. 4. This section shall not impair the effect of an exception, reservation or recital to limit any warranty of the grantor in the conveyance in which it is contained. 5. This section shall apply where the instrument by which the subsequent purchaser acquires his estate or interest is executed on or after September first, nineteen hundred sixty, except that where the conveyance containing an exception, reservation or recital described in subdivision one of this section was executed before September first, nineteen hundred sixty, this section shall apply only where the instrument by which the subsequent purchaser acquires his estate or interest is executed on or after September first, nineteen hundred sixty-one.