Why not ps -p 1 -o lstart= ? In real life the difference should be rarely visible. And then, did we want to know when it started booting or when it became

Why not ps -p 1 -o lstart= ? In real life the difference should be rarely visible. And then, did we want to know when it started booting or when it became usable. The latter would be rather tricky (even defining what it exactly meant by that).