Vishnupathi is as Holy as The Pradosha.
Pradosha is on the 13th day of the Lunar calendar
Vishnupathi is on the days when a new month is born as per Tamil Calendar.(selected months)
This corresponds to the Gregorian Calendar Months February,May,August and November.
These days are to be observed by Bhajans, Poojas and Parayans during the time indicated for Vishnupathi for every year in the Panchanga.
Visnupathi Days/Times for the year 2012 are as follows.
Kumbha Sankramana Vishnupathi Februray 13, 2012.
Vrishaba Sankramana Vishnupathi May 14,2012.
Simha Sankramana Vishnupati August 16,2012.
Vrichika Sankramana Vishnupathi November 16,2012.
The time is normally between 2.30 am to 2 hours afer Sunrise.
Please check Panchanga.
There are temples where one is recommended to worship.
For details, check the Link.
http://www.agasthiar.org/a/vpfeb2011.htm
You might check their Publication Agasthya Vijayam.
Sage Sathyaseela was ,because of his vow to speak the Truth at all times, became responsible for the death of a cow.
He was reborn as Sage Sajjana for the sin of being the cause the cow’s death, when he had his hands cut off for no fault of his own.
In the next birth he was accorded the greatest benevolence by Lord Vittala through the King
This happened in the Vishupathi Punyakala.
In another instance Lord Brahma, presuming that Lord Krishna was entwined in Maya because of his proximity to Gopikaas thus forgetting he was The Lord,(to remind the Lord He was The Lord) hid the Gopikaas and the Cows only to find that the Creation was going on as usual from Lord Krishna’s Flute when he started playing it.
This yet another instance of Lord Krishna performing Nishkaamya karma.
For more information on this subject please refer Agasthya Vijayam of march 1994 and may 1994 or check the Link provided above.
Panchanga for 2012-2013.
http://www.astroica.com/calendars/hindu-calendar.php?yr=2013&mth=1&lang=en&bc=1