The hourglass icon is like a countdown timer. Snapchat
what does the hour glass mean on snap introduced this icon to make sure that a user is aware that their Snapstreak with a fellow user is about to end and they need to take action to ensure that the streak continues. It’s basically a warning that you’re slipping in your performance and you need to step up your Snapchat game so that the hourglass icon can be replaced by the lit/fire icon again which indicated that you’re on your Snapstreak.