Hi Mona
The text of your ggradnfather's permission to emigrate tells me pretty much what I want to know. It makes sense to assume that 10 years is much too long. I did contact Hannovian archives to get the offical practice.
By mid 1800's I mean the years roughly 1840 to 1860. And of course regulations would vary from kingdom to kingdom.
If I get anything at odds with your info I will post it.
Max