How the puja muhurta is found
Each festival follows a time of day in the scriptures: Diwali in pradosh with a fixed (Vrishabha) lagna, Janmashtami at nishita (midnight), Ganesh Chaturthi at madhyahna, Dussehra at aparahna. We work out that window for your city.
The vidhi here is a simple home puja. Family and regional traditions differ — follow your elders or your priest where they guide you.