When should I book my class?
The more you practise, the more effective it will be.
That's why booking your classes as early as possible is beneficial. Most people book after their 20 week scan and before 32 weeks as the pressure to get things done increases.
Some people book just 2 weeks before their due date and still report seeing the benefits of the antenatal preparation and found the tools useful to enhance relaxation.
So the choice is yours.