Hi, this post came up recently, and I’m not sure it is accurate.
I couldn’t find any references to any of the Ubuntu Core components setting any mount options related to timestamp update settings (noatime, atime, relatime, or similar) on reference pc-kernel based images on amd64 architecture on UC16, UC18, UC20, UC22. Thus my understanding is that built-in kernel default is used which is relatime by default.
Custom kernels may change that in the kernel code, or inside initrd, but i am unable to find that. So I believe Ubuntu Core product, like classic, has been using relatime since it was changed in the Linux upstream kernel in 2.6.30 so circa 2009 or so.
W.r.t. reducing wear => do not that most of the system is readonly snaps on Ubuntu Core, meaning majority of files used at runtime are immutable and not update timestamps compared to a classic system. Thus the amount of files that get timestamp updates is fairly small during normal operation.