It is generally easier to learn how to program first, and after you've got the fundamentals down then start applying your knowledge inside a game engine.

how long does it takes to practice game development ?

Honestly, to become a master at the craft, it takes about a decade.

Learning the syntax of the language only takes a few weeks. This takes reading a good book on the subject, or a few web tutorials.

Learning the common function calls and how to use them takes about the same time. This is when many beginners say they have "learned to program".

Learning how to build whatever you want out of the parts available tends to take 2-4 years depending on how much you apply yourself. Often that is a degree in computer science. That's where most programmer students turn into entry level workers. 4 years of schooling and hobby work is enough to be a beginner in industry.

Learning the bigger patterns and practices take a few more years. These are usually spent as a junior developer, maybe the job title of Software Engineer I or Software Engineer II.

Mastering them to the point that you can figure out how to implement whatever anyone throws at you, that takes another 5 or so years of practice.

3D animation,game artist, programming,game designing

Those are five different careers. There was a time in the 1980s when a single individual would make the entire game, when graphics were a few squares on the screen, music was a few beeps, and game design was a few twists and turns on a level.

Those days are long past.

These days teams are much larger, and each role is filled with people who are skilled in their specific domain.

This is the online course I'm currently using. It'll cost you $15, but it seems to be thorough, and the instructor continues to update the course every week with more and more lessons. Now that Unreal 4 is free it's not too hard to begin learning it.

I have other question can I learn game developement without a degree in computer science ?

That's a tricky question to answer.

Some people can. Some people cannot.

You didn't fill out your location in your user profile, so I don't know if you're in a well-educated tech hub or a remote location with few schools. The rules for the Bay Area, Seattle, Austin, and similar are different than the rules for locations where there are few tech companies and only one game studio exists.

All programmers are expected to learn on their own. There are many fields where continuous learning is a requirement. You shouldn't trust a doctor who hasn't kept current with medical journals and practices, you shouldn't trust a lawyer who hasn't kept current with new laws and precedents in their area, and you shouldn't trust a programmer who hasn't bothered to stay current on modern practices and techniques. It is something you are expected to do on your own for your entire career.

But does that mean the college degree is required? That depends on location.

One of several things that happen in a degree program is that you are required to study topics you may not find interesting or enjoyable. Left to their own devices there are topics that people would not study on their own, and that list varies from person to person. Perhaps you would never study computer theory, or compiler theory, or databases, or networking, or certain algorithms, or certain data structures, or certain logic topics, or certain math topics, unless the school required you to.

For programming as a career, in many regions of the world a degree is a critical filter to get past HR. There are still ways to get jobs in those parts of the world, but finding your job will be more difficult and you will likely get less pay or a lesser position than your degree-bearing peers.

If you live in a part of the world where programmers are well-educated, then yes, you should look for a degree. If you live in an area where that isn't the case, that's up to your situation and location.