This is a Countdown Clock icon. We've made it in iOS style, first introduced in iOS version 7 and supported in all later releases up until now (at least iOS 11). This style is based on thin two-pixel lines and is optimized for 50x50 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 12,300 icons, all in the same style and quality.
It's the image of a clock face with the number "12" written in the center. Around the clock face are the dots where the numbers of a clock would go. The circle that encloses the clock face is actually a circular arrow drawn around the clock. The arrow is pointing counter clockwise to indicate time going backwards twelve hours.