Suggested readings: Building countdown timers in an email, Top elements of an email with a countdown timer, Best examples of countdown timers in emails
Countdown timers might look different on different devices. Every time an email template is opened in an email client, a request is sent to the timer service. In response, it provides a GIF-animated image that displays the time left to the target date and time.
The time might be different if the email is not opened simultaneously. Once an image is rendered, email clients usually cache it and do not send new requests on the second open.