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.
in fact there is no required time and you can be able to know it when you are focusing on making study about in bitcoin if you are may have a lot of time of making it you will never find oit the time that you already spent here.