Good luck, bro.
I think the warranty doesn't cover damage on cracked screen.
You need to bring it back to Samsung service center for repair.
How long, depends on their technician expertise and the parts they order.

The screen itself might cost a lot... ranging from RM300-500, through
the articles and feedbacks i heard so far...

My friend paid 500+ for a repair on the LCD screen because he accidentally dropped his S2. I think the price is within reasonable range.

any user here face up this issue?

Of course Samsung service centre, dude!

just piece of advice to potential s3 buyers, when you're buying the phone, IMMEDIATELY BUY A SCREEN PROTECTOR and A FLIP CASE for EXTRA PROTECTION. Don't delay, buy it straight after buying the phone.