Should be rather simple.
You can see how to programmatically create a timer if you look at the CreateTimerAction source code. They build a Timer object.
I would created an action handler on the node-exit of the start state which would take the entered date, and then do simple java date math
Date newDate = new Date( enteredDate.getTime() - 2419200000 )
Where 2419200000 is 4 weeks (in milliseconds).
Date newDate = new Date( enteredDate.getTime() - (4 * 7 * 24 * 60 * 60 * 1000) )
For the 4 weeks, 7 days in a week, 24 hours in day, so on and so on.
where can I find the createTimerAction????
Thanks a lot for the tip
Ok Ive found it.
I have another question, Where can I find the sintax for the due date, for the repeat and so on?
The same place I found it, the documentation.