A real GIF can't tick live forever — email images are static content. This mode instead bakes a short ticking clip (e.g. the next 5 minutes, second by second) into the GIF, which then holds on its last frame. Reopening the email later fetches a brand-new clip starting from whatever the real remaining time is at that moment.
Auto-refreshes every 5s so you can watch it tick. In a real email it only re-renders when the recipient opens the message — that's what keeps it accurate.
Use this if your ESP wants a raw image URL instead of full HTML (e.g. a "dynamic image" merge field).