I understand… I had this functionality (setting alarm on the particular date) on my old OnePlus 7 Pro with stock Clock (Oxygen OS 12.1). It was awesome. You could even set an alarm, check “Ring when powered off” or something like this, and you could power off your phone and let’s say I have a 6 AM alarm, the smartphone would automatically turn on itself at 5:58ish AM. I think every Clock app is based on “AOSP” clock project, so I think it depends on implementation and maybe hardware?