I've been trading options for over 10 years, and I never really had a discussion with anyone about when to enter option trades--specifically what time of day or even a specific day of the week. I usually trade the near-month options after the previous near-month options expire. I like to trade at the end of the day (from 3:45-4:15 EST). I like to sell bull put spreads (negative vega spread) when the VIX is up for the day. (By placing bull put spreads I have already decided that the environment calls for this particular trade). I also try to place the trades the Friday of expiration. Does any of this really make a difference?