Shivarathri is one of the most auspicious vratas for the devotees of Lord Shiva. The purANas explain the grand significance of this vrata. Especially Skandha Maha puraNa has the details of the way to observe the vrata

Maha Shivaratri – 4-Kaala Puja Timings

First Kala Puja – 6:30 – 9.30 pm

Second Kala Puja – 9:30 – 12.30 pm

Third Kala Puja – 12:30 – 03.30 am

Forth Kala Puja 3:30 to 6:30 am