what is the difference if I cook condensed milk for 2 or 3 hours?

[mousymouse]

have two different "recipes" to cook toffee. one says to cook the tin of condensed milk in a pot of water for 2 hours the other says 3 hours...
the only time I did it before I cooked if for 3 hours.

Either way is fine. You might just get a slightly darker caramel the longer it goes. Mind you, carnation kindly now sell a tin of already boiled caramel.