That depends on what your goal for the cue is.
If your goal is for it to feel right to you then a few shots is all that is needed to know if you like it or not, provided it has the same tip you are used to. This is because you already know what feels right, because what feels right is what you are already used to. And with that being said, what you are used to may not be what you would actually play best with.
If your goal is to improve your game, then lay aside "feel" for a moment and see if after some time you play better with the new cue. Does it help you on shape? Does it produce more or less cue ball action? Do you pocket balls easier with it? Does it stun the cue ball easier than your current cue? Do you win more competition games with it?
You have to try the same things with new tips to make a fair judgement.
So you might need to change the tip to the same tip you are currently playing with if you do not feel the cue provided improvement in your game.