Hello, I just finished A2 level and I am starting B1 soon. I wanted to know how much time should it take to finish it
That depends on how consistent you are in learning\study.
It may be worth your while looking up the success criteria for B1 and then breaking it up in to manageable components. This would allow you to have smaller learning objectives\targets with a greater chance of success. In other words, take it one step at a time. If you can work out how long it takes for each step, you can work out how long it will take to reach the next level.
II Hope this helps.
The same time you took to do A1.