creating anything other than the most simpletons of clocks without an RTC is highly questionable, unless its the trip than matters more than the destination.
I agree with that, but point out that a high proportion of the Arduino projects one sees are more about the trip rather than the destination.
At Maker Faire I saw an LED clock that displayed time in base 12 on a charlieplexed 9 by 14 LED grid. However accurate or not that clock may be, the maker was more interested in the fun of getting it to work then using it to tell accurate time.