Heads up: not everyone sees this ticking.

The live preview shows what you and tech-savvy Gmail recipients see. In reality:

• Apple Mail clients (with MPP on by default) — about half of all opens: see the timer image as cached at email delivery time. They don't see ticks; the visible time may be hours or days stale by the time they open the email.
• Outlook desktop: sees a static image (no animation expected).
• Gmail web/mobile: may refresh on re-open (best-effort; Gmail's image proxy is not contractual).

Every recipient can click the timer to open a live countdown page that's always accurate. The alt-text (for screen readers / images-off recipients) names the exact deadline date and time.