Meanwhile, I've found the following reliable selection of value in preparing this site (the superscript numbers indicate related puzzles):

• http://en.wikipedia.org/wiki/12-hour_clock (history)
• http://en.wikipedia.org/wiki/24-hour_clock (history)
• http://en.wikipedia.org/wiki/Modular_arithmetic (modular/clock arithmetic)

• http://www.code ranch.com/t/35405/Programming-Diversions/Exact-times-when-hour-minute (hands overlapping ²)
• http://mathforum.org/library/drmath/view/56835.html (hands opposite ³)
• https://sites.google.com/site/mymathclassroom/trigonometry/clock-angle-problems/clock-angles-between-the-minute-and-hour-hands-at-right-angles (hands at right-angles ⁴)
• http://en.wikipedia.org/wiki/Clock_angle_problem (angle between hands ^{5, 6})
• http://mathforum.org/library/drmath/view/68280.html (next same angle ⁷)
• http://www.urch.com/forums/gmat-problem-solving/90542-clock-angles.html (chosen angle after chosen time ⁹)
• http://www.ldlewis.com/hospital_clock/document/Hospital.doc (symmetrical positions ^{5, 8, 9})