It's an icon of the last hour reduced to a clock with a 1 on it. The 1 is centered in the middle of the clock. The clock also has a counterclockwise arrow running all the way to 11 in order to symbolize there is 1 hour left.
This is the Countdown icon for Windows 10
. Here we go. Optimized for 32x32 px, these are the simplest icons in the line style. Downloadable formats are PNG and SVG, among others. Icons8 icon pack is unique in providing a huge number of icons designed by the same team of four designers who create the new icons every working day in the same style and with the same quality. Same cool as the Bat Face, huh.