Hi Jean,
It`s working. Sorry for the false alarm. It seems it`s really not a good idea to work when your mind is not clear enought.
It might help someone, so I`ll post the steps I`ve done:
1. Create a new scene and an empty object and create a new FSM
2. In the first state(CREATE POOL) add the Pmt Create Pool action and type the name of the pool. Set "FINISHED" as the pool created event.
3. Add a second state(SPAWN) and drag the Pmt Spawn action. Type the pool name (the same you created in the first state and drag a prefab in the game Object field. I had an animated object prefab, just to make things easier to see the spawned objects. Set "FINISHED" as the Success Event
4. Create a third state(WAIT) and add the Wait action and set the time to 3s.
5. Link all the transitions:CREATE POOL-->SPAWN-->WAIT-->SPAWN
6. Hit play.
I also created a string variable with the intention to use the variable as the pool name but it didn`t worked. I`m too tired now to see why, maybe it`s a bug, maybe not.
Again, Thank You Jean.

Edit: I used Unity 3.5 and Playmaker 1.3.2