Short form: GNS530 - no go for sole, installed legal IFR clock
This is why it's one of the most obsolete, dumbest rules in the book, and why I could never be a DPE*.
Applicant shows up with a plane with 5 or more different time keeping devices on it or in it. Garmin 530, Garmin 430, GTX 345, iPad, phone, watch, kitchen timer, whatever. Oh, sorry, your plane isn't IFR legal because it doesn't have a device which is extremely seldomly used for any real IFR navigation anymore. We'll have to reschedule the checkride. Because it doesn't have a 40-year-old windup clock.
I don't remember the last time I used a clock for any non-training IFR navigation or ATC purpose where I needed the precision to the second. In fact, the only routine thing is IFR releases - but for that, I'm looking at my watch to see how much time I have left. And precision to the minute is sufficient.
Added to that, we now have all these GPS-synced clocks all around the cockpit, but nope, we still need that old user-set clock with questionable precision. A wind-up clock is even legal, when the billions-of-dollars satellite system we have is not.
The only thing you would really need to know seconds for is timing a holding pattern or timing for the MAP, both of which are pretty obsolete. And since even then you only need those for a couple of minutes at a time, you could easily bring up a page on the GPS. Or start your stopwatch. Or kitchen timer. It's not like that kitchen timer is too inaccurate.
Yes, it's 100% the rule. But it's an archaic, ridiculous requirement in 2021.
* I realized a few years ago that I don't have the personality to be a DPE. I did OSHA compliance for 9 of the longest months of my life and hated it. A man's got to know his limitations.