Please help me understand this , I read somewhere that entry at market open is so volatile, so when buy signal is triggered we should buy at closing time. Is it true ??
You can backtest that yourself without any backtesting software. Just get some historical charts of your trading instrument and review each trading day. Simply, trust your own test results instead of what something you read "somewhere" by "someone".
Best time??? After years of building your signals, testing and trading with small capitals, you'll become good at finding a good entry/exit point to suit your trading style.