2013 Shardiya Navratri Sandhi Puja
has special significance during Navratri Puja. It is done at the juncture when Ashtami Tithi
ends and Navami Tithi
starts. It is believed that Devi Chamunda
was appeared during this time to kill demons Chando
Sandhi Puja prevails for two Ghatis which approximately lasts for 48 minutes. Sandhi Puja Muhurta might fall at any time during the day and Sandhi Puja is done during that time only.
You might also be interested in complete Shardiya Navratri Calendar
and Durga Puja Calendar