Cartridge breakin ......how long?

Zd542, good cables , they can change dramaticaly for the better after 100-200 hours. I consider cables components.

120 - 150 hours with Koetsu. The suspension also needs break in, so you can put the tonearm on the LP, when the turntable is not in use.

I have a Soundsmith Aida and it took between 50 to 100
hours of playing time be patience you will be rewarded with great sound.

i like it when it's out of box just like new strings on guitar tho

IMO, it depends on the cartridge. My experience with various cartridges is between 20 and 200 hours to reach best performance.

ALSO, at least in the case of an AT OC9/(all of them), if they sit idle for a while (week or more), it may take them a few record sides to get back to optimum. Regular play keeps them loose.