You can do LLB after BBA.
Because doing that you can get to learn each and every concept properly. Going for sepetate course will help help ypu caver every concept be it of any concept of Administration or so. But if ypu prefer doing both the courses on same time then it might won't help you as the course will be designed in such a way thah either or any of the concept will get left out.
So prefer LLB after BBA.
Hope this answer will help you.
If you go for BBA LLB the course will be designed in the way that it can throw light on useful aspects of administration and law.
But when you go for LLB and BBA separately then in BBA you’ll learn whole concept of Administration neither concept would left and same way in LLB so doing both the courses separately will help you out in understanding both the fields deeply. Duration of the course - 5years BBA LLB /6years, 3 years for BBA and 3 years for LLB (1 year is a lot of time). It provides same flexibility as you can quit BBA LLB after 3 years with a graduation degree to pursue some other course.
Hope this helps!