On the first part of your question on how long it will take to make a transition I have to say it depends on the shooters desire to transfer honestly. If they see or feel the need they will make it happen. We are all influenced by others in some way or another, if we see our favorite instructor or our good friend or loved one using something new and doing well we start asking questions and become interested.
My wife is a great example here, she is very set in her ways in pistol shooting. Her belief is if it isn’t broken don’t fix it. How I have been transitioning her to become more proficient with the dot is to get her to use it every time we go out. I believe once you have decided to make the transition you are better off sticking to just the dot and not going back and forth. She has told me she really doesn’t like the dot as it seems to just move around and she still reverts to trying to focus on the dot as a front sight which is WRONG. I have to continually remind her that every one has “wobble”, and to target focus shoot, just let the “dot” hover in the middle of the target as you stare at the target.
I belive shooters new to running a dot that have trained to only front sight focus shoot will have a harder time. To become better, every time you practice whether live or dry fire, spend as much time as possible teaching yourself to threat focus and just let the dot be there, it’s amazing seeing a new dot shooter have their moment when it just happens.
The one thing I have seen and heard from my wife and others new with the dot is the “wiggle”. All shooters have this wiggle some just more than others. It can seem intimidating at first but with practice and understanding you have the same amount of wiggle with irons, the dot just let’s you see it more.
The pros of running a red dot equipped pistol far outweigh the negatives in modern defensive shooting. Look at it like this, what pros does a red dot bring to a rifle? All the pros are the same as are the negatives.
We tested some new shooters with irons and a red dot and almost every single one shot better with the dot. It was much easier explaining to them just put the dot on the target as you stare where you want to hit and press the trigger smoothly vs "Focus on the front site, equal height, equal light, etc etc.
As this has gotten long winded I’ll end with this, everyone has the ability to run the dot and with the right practice and attitude you will be a better and more proficient shooter, you just have to learn this,
Target/threat focus when shooting
Accept there will be “wobble” in the dot
Don’t let the dot intimidate you.
Hope this helps