Best resources to properly learn ORB? Looking for a fast but serious learning path

Thanks to everyone who replied to my previous post. After reading the responses, ORB seems to be the setup that comes up most consistently, so I’ve decided to focus on learning and testing it rather than trying to study six different strategies at once.
I have some basic knowledge of trading and markets, so I’m not completely new to trading, but I’ve never properly studied ORB or built a systematic ORB strategy.
I have a limited amount of time before a paper trading competition from October 7th to October 15th, so I’m looking for the most efficient way to learn it properly.
If you were starting with ORB today and wanted to become competent enough to backtest and paper trade it fairly quickly, what would you study?
I’m particularly looking for:
The best free YouTube channels/playlists
Good articles or written guides
Books or papers worth reading
A clear explanation of how to define the opening range
How to choose between 15m, 30m, etc.
Breakout vs. breakout + retest
How to use VWAP or volume, if at all
How to identify good vs. bad market conditions
Proper stop-loss and position sizing
How to backtest ORB correctly
I’m not looking for signals or a “magic strategy”. I want to actually understand the logic behind ORB, define objective rules, and then test those rules on historical data before the competition.
If you had to recommend only 3–5 resources to someone with basic trading knowledge but limited time, what would they be?
Thanks!