Bill, It's not a matter of conservative rating. Electrolytic capacitors eventually die of old age. The closer they are run to their rated voltage during their lifetime, the longer they last. When we are talking about low voltage at very low current like in this clock circuit, we are basically talking shelf life of the component. It will most likely go bad in x number of years whether it is in a Mercedes clock, or sitting on the shelf at Radio Shack.
If you want to experience the thrill of a really bad electrolytic capacitor, if you go dig up some old tube-type radio that has been in the attic since the 50's, it will probably have some paper electrolytics in the 150 to 250 volt neighborhood. There is a good chance when you power up an old radio like that, there will be a nice BANG, accompanied by paper and tinfoil confetti. Pretty neat entertainment!
2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg
And remember folks, Only You Can Prevent Hilliary.