How to reproduce:
place down a bunch of copper related blocks
set the random tick speed to a ridiculous number
compare this to a standard time copper takes to oxidise
Note: this may or may not be WAI
MC-203591
Oxidation of the copper block and all its variants is unaffected by the randomTickSpeed gamerule
Resolved
Works As Intended
10
Can confirm.
"It takes 50-82 Minecraft days (in loaded chunks) for a copper block to oxidize one stage" makes it sound like something that would be affected by randomTickSpeed because of the range, but it could also be that Mojang has not decided specifically how long it should take.