Because Custom Lists are stored in database tables, the system must make changes to the database structure in order to create or update any custom lists. Applying this change will cause the system to pause (for all users) for a few seconds, usually less than 10 seconds. 

This will only happen once all the approvals are complete, and only if changes were made to the forms in checklists. After approval, rather than just returning to the updated page, it will apply the changes and refresh the page - meaning it will go gray for a few seconds while it applies the changes and restarts the server process.

You will not see the actual list in the Lists tab until the changes are approved.

Note: Because of the possibility of this interfering with use of the system, you can set an approver on the Custom List Settings window, so that someone can approve that change who will understand the impact it may have on system operations. (For example, they may decide to delay approving until they know the system is not under heavy load, to reduce disruption).