No one can provide exact and correct answers to your questions because things will always be different for different people. To become a blockchain developer, you must be a developer first because it's important to be a programmer if you want to become a developer in any programming language.

When you ask how long it is going to take and whether 6 hours a day is enough for it or not, I would say that it depends on what you currently do and also what you like in general. You can't become a gamer if you hate playing games. Similarly, you can't become a blockchain developer if you don't have a general interest in the field and in technology as well.

It also depends on how sharp you are. Some people might learn a thing within a day, but for some, it might take them a week.