Well, it's quite easy to double it when you start with freediving. Even more. As I was told, everybody can make 4 minutes with the practise.
Example: there was a guy who did something over 1 minute in the beginning of the FIT course. After two short days of training of proper techniques he managed to hold the breath for more than 4 minutes!
However this is something a lot of people can do, after that it becomes harder and harder to improve.
I do not think it's possible to double 4 minutes in any term of short time. However I think that it's realistic that you could do 8 when training properly and regurarly - but it will take more time.
Ooor, you are one h*ll lucky ba*tard and you will manage in one month and everybody will ask you for know how.
