What’s wrong with this sentence?
“She stood, restlessly, by the window looking out over the rear garden for over an hour.”
The quoted sentence has a misplaced modifier. In the end position, the adverbial modifier for over an hour appears to be modifying looking out. To improve the sentence, move for over half an hour to the front position, close to the verb it modifies.
For over half an hour she stood, restlessly by the window looking out over the rear garden.