Before vs until

Could someone tell me what they think about the following :

if it the right word that's chosen :

ex1)He should be in hospital for at least three weeks before he is allowed to go home.
ex2)He should be in hospital until he is allowed to go home.

ex3)It will take 50 years or even a century before the species restores itself to its number of
a decade ago.
ex4)It won't take as many as 50 years before the species restores itself to its number of a
decade ago.

ex5)I will stay here for 6 months before I go back to my country.
ex6)I will stay here until I am asked to leave.

thanks