Putting in the hours, backtesting or paper trading or analysing previous chart data?

Many successful traders and YouTube mentors, all say that you need to put in the time to get good at understanding the charts. Some say that you have to put in 100s of hours. What does this mean, 100s of hours of backtesting? Or just going back in time to analyse the charts and see which trades could have been taken?, or just forward testing/paper trading?
I use optimal trade entry by ICT. As it is a strategy from a very experienced trader, is it necessary to spend that amount of time backtesting it ?

its not about understanding 1 minut or 6 minut charts… there is no one system exist that work on any instrument… trader must understand global picture first and then go into the smaller timeframes with single stocks…

@Win-Algo What do you mean by Global picture?

understanding global trends not only one single stock