It shouldn't be a defined amount of time and should be when you can. You should be able to constantly be learning about Bitcoin and cryptocurrencies in general. Researching could just mean looking at this forum and taking in the knowledge of other posters here.
I agree with the statement, because actually, we really don't need to measure the time in researching about bitcoin. That depends on the person, if he is more focused in learningore about bitcoin, he gives more time to it, on the other hand, people who focus less on bitcoin because of the physical activities they need to do, tend to give less time learning about it.