A special kind of watch

Display the complete time or date with just 12 colored LEDs. I have set myself the task of creating an electronic binary clock with as few display elements as possible. Each unit of time (hour, minute, second or year, month, day) should be displayed with only four LEDs. With four LEDs, however, it is only possible to display the number range from 0 to 9 in BCD code. One goal was to use only four LEDs to display the maximum number range from 0 to 59 required for hours and minutes.