There are few important points one need to consider while selecting Diwali Pujan muhurta -
1. Pradosh Kaal
The best time for Laxmi pujan is 3 muhurta (144 minutes) from sunset. Three muhurta (6 ghadi or 144 minutes) period everyday is called Nitya Pradosh and considered auspicious. Few people consider sunset time +-144 minutes and others also consider sunset time +- 72 minutes. In my opinion, closer to sunset time, the most powerful be the muhurta.
2. Lagna (Ascendant)
In my opinion, ascendant is the most important part of muhurta selection. It is said that if Lagna is good, one need not to worry about other doshas. Generally sthira lagna (Vrishabha - Taurus, Simha - Leo, Vrishchik - Scorpio, Kumbha - Aquarius) are considered most auspecious for the Diwali Pujan. We need to judge chart of the time according to astrological principles e.g. there should not be planets in 6,8,12 houses. In case we have to perform puja during that time, we should pray for the afflicted planet first and that peform the pujan. This is called shuddhi-karma.
3. Chaughadia or Chogadia
24 hours are divided into 16 equal time divisions and each divsion is known as Chaughadia. These 16 divisions are allocated to 7 choghadias as follows -
1. ‘Udwega’ - owned by Sun - Bad
2. ‘Amrit’ - owned by Moon - Good
3. ‘Roga’ - owned by Mars - Bad
4. ‘Laabh’ - owned by Mercury - Good
5. ‘Shubh’ - owned by Jupiter - Good
6. ‘Chara’ (or 'Chala') - owned by Venus - Medium
7. ‘Kaala’ - owned by Saturn - Bad
One should pick a good chaughadia for diwali pujan muhurta.
It is important to understand that all above mentioned points - pradosha kaal, lagna and chaughadia change for each location and that is the reason there is no standard muhurta for all the cities. In other words, diwali pujan muhurta for Delhi will not be the same as muhurta for Agra. It is important you consult local panchang, local news paper or local astrologer so that you know exact muhurta for your location. You can also use http://www.astrosage.com/ which can give you location specific calculation. Though for someone from non-astrological background it will be difficult and I would recommend consulting local newspaper or local astrologer.
1. Panchang & Diwali Muhurta for Laxmi Pujan
2. Diwali Pooja: Some Important Points to Know