Shiva Purana
दिनद्वादशकं वा ऽथ दिनषट्कमथापि वा ॥ तदर्धं दिनमेकं वा व्रतसंकल्पनावधि ॥ ९ ॥
It may be twelve days or six days. Half of that or one day until the resolution of the vow.
english translation
dinadvAdazakaM vA 'tha dinaSaTkamathApi vA ॥ tadardhaM dinamekaM vA vratasaMkalpanAvadhi ॥ 9 ॥
hk transliteration by Sanscript