1. The amount of time alimony is paid
Do you mean child maintenance? Or alimony to wife? For alimony to wife, if you admit fault in the divorce proceedings, then the alimony carries on for the rest of her life or until she remarries. If it's child maintenance itt stops once the child finishes full time education or is working and earns enough to support themselves. But in theory it can be started again at any time in a child's adult life, if for example they lose their job and need help from parents or if they decide to return to college and do a masters when they're 25.
2. The amount that is paid
No, no upper limit.