Shani Astami is an auspicious vrat dedicated to Lord Shani and Lord Venkateshwara (Balaji). In March 2012, Shani Ashtami vrat date is March 31. It falls in Shukla Paksha of Chaitra month.
Ashtami will be till 1.42 PM on March 31. It is the auspicious time for Shani Graha Shanti Puja, Shani Thailabhishekam, Venkateshwara Vratham, etc.
Here is list of Shani Astami Vrat 2012 dates – Link