Keep a backup
Duplicate the HTML file. If the snippet eats the layout, you have a way back. This is especially true on static funnel pages.
Put it near the thing it affects
A countdown belongs next to the offer, not in the footer. A redirect belongs only on a page whose job is to send people along - never on a quiz mid-flow.
Check the phone
Old scripts assume wide screens. If it overlaps the CTA, it is not shipping. The download is optional. The click is not.