Hä?! A clock shows the period of time we are currently in. A clock only showing hours would for example indicate that we are in the 14th hour of the day, for the entire duration of that hour. That is not an error. Similarly, a hh:mm clock will show the hour and minute we are currently in for the duration of that minute.
No clock can display the exact current moment of time. That would require infinite digits, and even then those will be late, since lightspeed will ensure you recieve the femtoseconds and below really late.
What time it is, is just made up, it's something we can decide freely through social power, as evidenced by timezones and daylight savings and leap seconds.
Commonly the resolution is something like minutes or a few of them, that's the margin we'll typically accept for starting meetings or precision in public transport like buses.
The utility of femtoseconds in deciding what time it is seems pretty slim.
Yeah, I think labelling it "error" is a bit of a strange way to look at it to be honest.
It's only error if you're trying to measure time in seconds, but are doing it with a clock that can only measure hours and minutes. If you want to know the current minute, then a clock that can measure minutes it is 100% correct.
It's an interesting thought experiment, but really all it's saying is that half of the time 10:00 is closer to 10:01:00 than 10:00:00, but this imply you care about measuring time to the second which prompts the question why it's being measured in minutes?
To be charitable, I suppose in the real world we might occasionally care about how close 10:00 is to 10:01 in seconds, but the time shown on phones can't tell us that so on average we will be about 30 seconds out.
No clock can display the exact current moment of time. That would require infinite digits, and even then those will be late, since lightspeed will ensure you recieve the femtoseconds and below really late.