How long will it take me to get to B2 as an absolute beginner?
Each course level consists of two half levels. You need 4 weeks per half level, so 8 weeks per complete course level.
Here is an example:
A1.1. - 4 weeks
A1.2. - 4 weeks
A2.1. - 4 weeks
A2.2. - 4 weeks
Etc.
You can find more information here.