Hi freddy,
While the Terry Maas book has some good stuff in, it has very little on training. I remember buying it years ago hoping to find some training techniqes to improve my freediving and it had squat.
Dry statics are safe to practise on you own, in the pool you need a buddy. To practise breatholds, I guess at least a couple of times a week up to once a day.
As for how long it will take, that really depends on the person. A friend of mine was a complete beginner and he did over 4 minutes the first time he tried a static in the pool. After 4 pool sessions he did 6.25 !
Something I still haven't beaten yet. Another guy I know who has trained for a couple of months, has only gotten to around the 4 minute mark (wet static). I think some people must have some genetic advantage in Statics. But the biggest part of it is mental, being able to relax, and not being scared to push it...
Also experiment with different warm up routines, some things work well for some, but no for others.
Cheers,
Wal