For critical positions in your opening repertoire:
- How many PLY do you recommend to let the engine run on a single move
This will depend on many factors such as the actual position, how you use the engine for opening analysis, etc
If the engine gives a decent advantage (let's say +-2 or so), there is usually not much point in having it calculate down to mate. Other than that opening analysis with an engine is tricky and should certainly not be automated. Engines are useful for pointing out tactical mistakes in openings and can be useful in evaluating midgame/endgame positions that result from some opening lines.
However at least currently you cannot expect engines to give you the absolute best line from say move 5 in any opening. In many openings engines give an evaluation of +0.6 or so even though experience shows that positions are perfectly playable for both sides.
Also human interaction is needed to evaluate how playable the position is for a human: e.g. you might have an equal position where you are required to find 10 only moves or so; this is not what you want to get into.
- How long does it take you time-wise to reach this?
Depends on position, computing power and perhaps other factors.
There is no definite answer.
That really depend on how seriously you think you are. Serious player would let a machine run for a whole day for just a single position. Casual players would just run it for about a minute. If your position is quite and equal, you might get the similar moves, so extra computing power would be useless.
Again, that could be a minute or that could be a day.
Please note running the machine for hours is generally waste of time if you don't know what you're doing. Serious players don't analyze every position deeply, they know when to do it and when not to do it.
