As per the Puranas, the Ramayana War was fought for a total of 87 days with occasional halts for a period of 15 days, thus making the number of days of actual fighting 72.
The starting tithi is: Māgha Śukla Dvitīyā
(The second tithi of the bright half of the month of Magha)
The ending tithi is: Caitra Kṛṣṇa Caturdaśī
(the fourteenth tithi of the dark half of Chaitra)
Quoting the relevant extract from the Padma Purana:
माघशुक्लद्वितीयायाश्चैत्रकृष्णचतुर्दशीम्।
सप्ताशीतिदिनेष्वेव मध्यं पंचदशाहकम्॥६८॥
युद्धावहारः संग्रामो द्वासप्तति दिनान्यभूत्।
During the eighty seven days of the war which began on the second day of the bright half of Māgha and continued up to the fourteenth day of the dark half of Caitra, there was a cessation of hostilities for fifteen days, thus the (actual) war took place for seventy-two days.
— Padma Purāṇa Pātāla Khaṇḍa Adhyāya 36, Verses 68-69a
Notes:
- Exactly same verses are found in the currently available Skanda Purana too. One can locate it in Chapter 30 of the Dharmaranya Khanda of the Brahma Khanda of the Skanda Purana.
- A reading of the chapter and the dates, reveals that the dates are as per the amanta panchanga (month ending with Amavasya, and new month starting from Shukla paksha, like the South Indian one but unlike the present North Indian one where Krishna Paksha comes first)
Shukla Paksha
instead of traditionalKrishna Paksha
.