It depends...
If they have already made the decision to kill you, you will likely lose.
If they decided to shoot at the first sign of resistance, you will likely lose.
Their decision cycle time in those cases is past or already shortened. Most people cannot draw and fire much quicker than 1 second. From concealment, a person that does not regularly practice will be closer to 2-2.5sec. Reaction time for a decision that has already been made (e.g. fire when they move quickly) is going to be in the .5-1sec range. So, your concealed carrier will probably lose by at least a second, here.
Now, that assumes this is a pre-made decision, and the opponent picks up on the action quickly. There are plenty of distractions you can make to slow their recognition of resistance. Getting them talking or dropping/throwing a wallet are very common ones, and may buy you an extra .5-2sec. That can make the difference. Futher, concealing the first part of your draw stroke can buy you another .5-1sec, if done right.
So, if a criminal is not expecting resistance, has not decided to fire on the first sign of abnormality, you distract them, and conceal the first part of your draw stroke, you will likely have the advantage.
...sure not a "sure thing," but if you start adding time on their end while reducing yours, you may gain the advantage.