you cannot establish best time for day trading, since it all depends upon the market sentiments and the market conditions
if suppose the market is expecting a rise, it is not necessary it will be at top in the morning or in the noon or at the end it may be at any time and the day traders will keep you guessing whole of the day. it is up to you to decide whether a scrip has reached its peak/ bottom at a particular time. it may also be possible that if you are expecting a rise in the market (due to some better news or some sentiments in the market) the market may start with the bottom and rise or it may start at peak and then slowly come down but at a particular level. it may also be possible for remaining it volatile thoughout. it all depends upon the early one hour.