I know you said no Windows — and I haven't used Windows in over a decade.
But back when I did use it, it had a nifty feature where if you create a new empty text file in notepad and save it as .LOG, then each time you open that file it'll append the timestamp. Something like that (my memory about it is a little hazy).
Yup almost.
Its not how you save it, its about having the .LOG in the first line. Hit enter and save it.
Now everytime you open that file, it will append the the timestamp to it.
I was a Windows dev (now retired) and from the late '90s that's exactly how I kept a daily log: a Notepad file with .LOG as the first line gets date & time appended every time its opened. Notepad used to have a rather small filesize limit, so I'd just make a new file every month or two. Later I used TextPad [0] a commercial Windows editor which also supports the .LOG-as-first-line system, as TextPad can handle arbitrarily long files.
But back when I did use it, it had a nifty feature where if you create a new empty text file in notepad and save it as .LOG, then each time you open that file it'll append the timestamp. Something like that (my memory about it is a little hazy).