Oś czasu and other 68,000 icons from Icons8 icon pack follow the visual guidelines of the operating systems: Windows, iOS, Android KitKat, and Material. PNG format is free up to 100x100 px. Icons are availble for download in PNG and vector (SVG, PDF, EPS, and more).
The Timeline icon is comprised of four lines and three circles. Three horizontal lines are evenly spaced and extend from the right side of one vertical line. On the top horizontal line, a small circle is placed just left of the middle point. On the second line, the circle is near the right edge, and on the third line the circle is on the left end, closest to the vertical line.