First, bullet time is primarily associated with 'The Matrix', where people do things not possible in real life, like reacting to bullets being fired and dodging them.
Next, Batman isn't super-human, nor does he have any physical/mental capabilities that a normal human isn't potentially capable of with some training. The idea of the character is that he's a person driven to obsessive lengths to achieve justice and also happens to have the resources available for the required gadgets.
Therefore, a guy jumping into a speeding car as it flies over a gap results in a suspension of disbelief for me, partly because a) I doubt that it's possible in real life*, but mainly because b) a normal (albeit very capable) human being would opt for a safer tactic and c) while Batman would probably consider sacrificing his life in order to avert a major catastrophe, I very much doubt that he would want to go down in history for prat-falling to his death when such a show-off stunt inevitably goes wrong at some point.
I personally filed that particular scene under "stuff that's put in to the game to impress early teens".
* - A stunt artist might be willing to do something vaguely like this if the car is designed in a certain way, the exact parameters of the stunt are pre-determined (how much of a gap, the exact speed of the car, the ramp, etc), safety measures put in place in case it fails, and that they are able to practice the stunt (or elements of it) a multitude of times first. None of which apply in the scenario that I have a problem with.