No an enquiry is just that, like you said - an enquiry!
Once you have responded initially, the clock stops ticking and further communication or lack off does not affect your response rate nor impact you negatively. Personally I no longer pre-approve because on a couple of occasions when I pre-approved for dates two months ahead then changed some of my rules/ description and prices in between, when the guest eventually returned neared the time to make the booking, although they had to request a new pre-approval as the original had expired after 24 hour, they still got my old rules/ prices and description so I never put myself in that position anymore. Also I don't decline as too many declines eventually impact your status.
The only time I accept or decline is when it’s a Request to Book.
BW, Ama