Hi and welcome to the community!
Covers are approved by admins, so the time of approval can vary depending on the quantity of edits submitted and the time they have on their hands. They really do their best, but sometimes they don't have the time to review them within 1-2 days.
Just for your information, when the edit is approved or rejected, you will have a notification on your collection page
The triangle icon with an "!" on the upper-right corner will become yellow.