Kamasutra 2.1.37

2.1.37

mṛdutvād upamṛdyatvān nisargāc caiva yoṣitaḥ/
prāpnuvanty āśu tāḥ prītim ity ācāryā vyavasthitāḥ//

At the first time of sexual union the passion of the male is intense, and his time is short, but in subsequent unions on the same day the reverse of this is the case. With the female however it is the contrary, for at the first time her passion is weak, and then her time long, but on subsequent occassions on the same day, her passion is intense and her time short, until her passion is satisfied.