Apps created from Hex projects have a sense of versioning, including a currently "Published" version.
This published version is the only viewable page for users with App User permissions.
The Publish button will appear anytime there are unpublished changes in a project.
Clicking this button, you will be presented with the option to publish your changes, along with a live preview of your changes and a link to the currently-published version of your app for reference.
You can view and revert to past versions of a project using the Version control dialog.
Seeing an error in the Publish preview, but you just ran things and swear it works? Apps (and previews) always run every cell in your Logic top-to-bottom with a new kernel. This means there may have been now-deleted variables lingering in your personal kernel, leading to errors in the new kernel. Try to go back to the Logic View and Restart and run all to pinpoint the problem.
You can use Hex to schedule runs on a periodic basis. It's important to note that scheduled runs will execute the currently-published version of the logic, which may differ from the version you're viewing.