It is difficult to establish mythological epics on chronological and other related basis,yet i am herewith presenting ancient process of calculation of months and days.The various Hindu calendars are based on eras and epochs. Generally, the Hindu calendar follows the lunar year that consists of 12 lunar months. A lunar month has two fortnights. The following lists mention the Sanskrit names of the Hindu months, days and lunar days and their correlation with the Gregorian calendar.
Read more about the Hindu Calendar System

The Hindu Months

Names of the 12 months of the Indian Civil Calendar and Correlation with Gregorian Calendar
Chaitra (30 / 31* Days) Begins March 22 / 21*
Vaisakha (31 Days) Begins April 21
Jyaistha (31 Days) Begins May 22
Asadha (31 Days) Begins June 22
Shravana (31 Days) Begins July 23
Bhadra (31 Days) Begins August 23
Asvina (30 Days) Begins September 23
Kartika (30 Days) Begins October 23
Agrahayana (30 Days) Begins November 22
Pausa (30 Days) Begins December 22
Magha (30 Days) Begins January 21
Phalguna (30 Days) Begins February 20

The Hindu Days

Names of the 7 Days in the Hindu Week
Raviãra: Sunday (day of Sun)
Somavãra: Monday (day of Moon)
Mañgalvã: Tuesday (day of Mars)
Budhavãra: Wednesday (day of Mercury)
Guruvãra: Thursday (day of Jupiter)
Sukravãra: Friday (day of Venus)
Sanivãra: Saturday (day of Saturn)