Pradhosam  is observed in reverence  to Lord Shiva . Pradhosa  time  occurs on trayodasi (thirteenth moon day) between 4.30 p.m. and 6.00 p.m. It occurs on  13th day from full moon day and new moon day .Praying to Lord Shiva during Pradhosa  time relieves us from sin and leads us to moksha.

Purana says:

While Devas and Asuras were churning for  amudha  from Kseerabti  milk ocean employing the serpent Vasuki and the hill Mandhara, initially poison known as Halahala poison came up. Lord Shiva saved them from the effect of poison  by consuming it . On  Dhwadhasi day,  i.e., twelfth  moon day , amirtham came and Devas and Asuras started celebrating their victory without thinking and thanking Lord Shiva who saved them from the ill effect of deadly poison.  Next day    i.e. on the thirteenth moon day they realized their mistake of not praying and thanking Lord Shiva  and prayed to Lord Shiva seeking his grace. Then Lord Shiva forgave them and danced between the horns of holy bull, Nandhi. The time when Lord Shiva performed this cosmic dance is called pradhosam time.

It is generally  believed that  performing abhisekam  during the pradhosa time  to Lord shiva with  Milk gives long life ; Ghee gives Moksha state; Curd bestows us with good children;  Honey graces  with  melodious voice  ;  Rice powder  relieves us from debts; Sugar cane juice  graces us with  good health ; Panjamrutham gives wealth  ; Lemon  removes  fear of death  ; Sugar removes enimity  ; Tender coconut  gives  enjoyment  ; Annam  gives  majestic life ; Sandal  gives  Lakshmi’s grace.