Questions about EV modification -

First, please search the forum for "EV mode" and "EV mod" and you'll find a plethora of information.

Acceleration while under EV mode is better than you can get on battery alone when not in EV mode but much less than with the ICE boosting. Acceleration under EV mode is not recommended b/c it is significantly less fuel efficient than when using the ICE as the car is designed.

Severe overuse of EV mode could, probably lead to an earlier death of the battery. However, used the way it's designed...occasional use to move the car a short distance, to shut off the ICE when approaching a stop, to prevent ICE start up when moving in heavy traffic or while in line for a drive through, etc. then there should be no issues at all.

There is no way to say how long until the ICE kicks in...it depends upon what you're doing. If you accelerate hard, maintain a high speed (up to 33mph in EV mode) and are going up a hill the battery will drain faster and the ICE will kick in sooner. If you're going very slowly, down hill, and don't hit the EV button until you're up to speed you could coast for a couple of miles from a high charge before it drains enough. However, the simple fact that you're asking this question leads me to think your expectations of the EV mod are outside of what it's designed to be used for. You really are better off both for the sake of the battery and for fuel efficiency and for emissions to let the car run normally most of the time than to try to override it with the EV mode...you'll ultimately get worse mileage.