Which option fits best in the following question.I cannot see any difference in meaning.
We seldom had the ____________ to get out for an evening in town.
According to the Longman Dictionary of Contemporary English, permission is an uncountable noun. It is not used with 'a', and is not usually used with 'the' unless it is followed by 'of' e.g.,
So opportunity is the right choice.
The meaning is quite different: opportunity implies the time and physical ability - it could also include permission, but that is rather lower on the list of elements that might contribute to it than physical limitations.
But idiomatically, "permission" is nearly always used without an article, where "opportunity" is usually (though not always) used with an article. So "had the permission" sounds very strange.