So. How accurate does Minecraft redstone clock compared to actual clock ?

Well. I did say it is quite accurate. Still halfway done. Not yet build the core for the hours digit.

Bit challenging to build as it doesn't use any piston to reduce lags. Only uses repeater clocks and comparator for logic gates. Some of other redstone componens too but pistons. Or any component moves a block.

Fun fact. 10 ticks or 10 repeater in series in 1 tick mode is equal to 1 second.