I’d say nowadays the standard routine is about 2 hours of boxing training earlier in the day, followed buy a strength and conditioning session afterwards. Usually about 5-6 days a week. Probably only 3 or 4 days of actually pushing it at 100%.
Not a detailed breakdown or much information on actual boxing training, but Joseph Parker's road to champ series on YouTube os great for showing what his camp looks and feels like. So a lot of the intangibles that don't really come across in other media or workout plans or descriptions. Plus it does show his S&C training, nutrition and the overall structure of the camp and team involved.
I've heard Joshua studies a lot outside the gym. Philosophers. Big time gangsters. He's a student of the game and of life.