If you go to one of the larger modular schools they'll be able to give you an idea. Somewhere like Cabair or Multiflight. The CPL requires a number of theory exams to be completed, how you study for them depends on the training provider. Some have scheduled classroom time, others leave you to self study with "crammer" sessions before the exam.
Have you researched the differences between the CPL exams and the forzen ATPL requirements?