What did ancient Egyptian sundials and shadow clocks do that helps explain the 12-hour clock face?

Answer: They split daylight into twelve

They split daylight into twelve ✓ — Correct. Egyptian timekeeping carved the sunlit part of the day into a 12-part pattern before modern clock faces existed. That is why the later 12-hour dial looks less like a designer's shortcut and more like an old daylight-counting habit made durable.

They measured seconds precisely — That answer gives ancient instruments too much precision. The cited Egyptian evidence is about hours and daylight divisions, while minutes and seconds entered ordinary clock displays much later. A sundial shadow is powerful, but it is not a stopwatch.

They ignored changing seasons — This misses the most interesting twist. Early daylight hours did change with the season, because sunrise-to-sunset was being divided into shares. The 12-part habit survived even though the length of each early hour was not yet fixed.