When updating a site's template files or making changes to the design, an administrator may find that the changes are taking more than the 15 min suggested delay.
If you are trying to view the template changes by clicking on the file through Administrator> Site Design, the file you are viewing could be a cached version. It is best to go to the website from the front end, not the file, in order to see the most recent changes. These could take up to 24 hours to propagate, but it is uncommon for it take that long.
For faster file updates, it is best to rename subsequent uploads, so no 2 uploads have the same name. This will prevent you from seeing a cached version.