It is usually better not to judge a promotion based only on the first 24 hours.
Readers may discover your book over several days, especially when recommendations are personalized or when subscribers open newsletters later.
The Fussy Librarian provides post-promotion reporting so authors can see how reader activity develops beyond the scheduled date.
If your goal includes series read-through, reviews, or sales of other books, those effects may take even longer to appear because readers need time to download and read the promoted book first.