How many hours did it take you to undertsand all of the concepts on each cause areas?

Yeah, there might be no end to how much you can understand about EA (or, more generally, stuff about the world that's relevant to altruism).

I certainly have my own blindspots but when talking to many other EAs I do notice that there a lot of topics they seem unfamiliar with:

• The extent of the uncertainty we have about the philosophy of mind
• Chances of being in a simulation/percentage of copies in a simulation and how that affects the expected value of various actions
• Philosophy of science/core assumptions behind how one thinks the world works
• Views of people in other parts of the world/society. 
• Relatedly, how futures led by influential people in other countries might compare to futures led by influential people in their own countries.
• Reasons to think that there are quite a lot of things that are low tractability
• Noticing how they came to be who they are/their place in history
• Impact of various activities on wild animal suffering

I don't claim to know everything about the above. And of course, others who know more about other things might notice that there are a lot topics I'm unfamiliar with. Some topics I haven't really thought about that much relative to a lot of people working at EA organizations:

• Anthropics
• Alien civilizations, how that affects priorities in longtermism
• Ethical theories that are super formalized (my moral anti-realism doesn't make me that motivated to look into them)
• Acausal interactions and decision theory

I don't think there's a single cause area where even knowing the sum of all human knowledge on the topic would mean you fully understand it