Unfortunately I'm not sure how much help we can be here... And especially me since I actually use a UDS rather than electric. But I'll give it a go anyway...
The answer is pretty subjective. First of all, are you soaking the chips at all? Soaking the chips in water prior to putting them in will help them last longer. If your electric smoker can use wood chunks, I recommend them. They last longer than the smaller chips. In terms of when to replace wood chips, replace them when they stop smoking or are burnt up (this may not happen in an electric smoker... Hopefully an electric guy will step in here). Finally, it isn't really necessary to keep adding smoke after a certain point IMO. People will have differing views on this as is with most aspects of BBQ, but for example I don't get any noticeably more smoke flavor after my butts hit 165 internal temp.
Above all else, if the Q you're turning out tastes good and smokey (to YOUR PERSONAL preference), then don't change your process! If you want more smoke flavor, I would replace chips more often or use more chips to begin with. If not, keep doin what you're doin! Experiment to find your favorite method, own it, and love it! Good luck.
