I’m getting some serious deja vu. Same kind of questions, same people replying, same kind of replies.
So, that’s “odd”.
Anyhow, to be brief: “full body training vs bodypart splits” is one of the biggest debates in bodybuilding. There have been tons of articles and threads about the pros and cons of each. There’s no right answer or best way.
You should train a bodypart for as long as you need to. Your goal will dictate the volume, intensity, load, exercises, and frequency. The specifics will vary a little depending on the bodypart (if you are even doing bodyparts, considering the first question), but in general, the “out of the gym in 60 minutes rule” isn’t considered as important as it used to be. Go in, train appropriately, and leave when you’re done.
Training to failure is another thing that’s often discussed/debated. Training up to, or beyond, muscle failure used to be the way to train for size, but the last few years people seem to be noticing more overall benefit from keeping a rep or two in the hole most of the time and treating muscular failure like a special technique.