I feel like there is a slight difference between "under many minutes" and "in many minutes" in the following sentence, but I cannot tell what or why. Could anyone help, please?
The context is:
Elizabeth has just told her mother that she has been engaged with Darcy.
When her mother went up to her dressing-room at night, she followed her, and made the important communication. Its effect was most extraordinary, for, on first hearing it, Mrs. Bennet sat quite still, and unable to utter a syllable. Nor was it under many, many minutes, that she could comprehend what she heard, though not in general backward to credit what was for the advantage of her family, or that came in the shape of a lover to any of them. She began at length to recover, to fidget about in her chair, get up, sit down again, wonder, and bless herself.
from Pride & Prejudice