If time from 1 PM to 6 PM UTC is busiest time on Ethereum blockchain, people would avoid those hours if they want to save transaction fees. Busiest means highest fees.

I don't know it is best to trade or worst. The article writes about Ethereum hourly fees. Trading is correlated to price changes, big or small. Changes should be big but it is not applied for all trading strategies. If you use Scalping trade, you don't need to have big changes.