These stamps are original products by stationery brand Mizushima.
The popular Clock Stamp features an empty analog clock for you to fill in its hour and minute hand. This provides a way to clearly label the time of an important appointment, or fill in a time span of a certain activity that day, just to name a few examples.
The Schedule Circle Stamp provides a 24-hour pie chart for you to color in each piece of your daily schedule for an easy-to-see graphic of your time allotment. You can also draw lines to denote times of certain appointments, or use the circle as a general pie graph.