How long does it take to have a perfect 800+ credit score if I'm regular on my payments?

I have seen people achieving 750+ score in 2 years. So, it can be achievable within 2.5 years. Try for it! At least it won't cause any harm. Even if you don't achieve this magic figure, you can enjoy a good credit score which will help you maintain a good lifestyle.

I guess it'll take approximately 3 to 3.5 years.

Between 2 and 3 years.

Look it takes time. Make sure you don't miss any payments. Also check your credit report. if you get any error, then dispute it.