If your 4S cannot do 2 hour of use then either the battery is busted, or the iPhone app needs improvement due to massive battery drain. Neither of those are valid reasons not to get rid of the timer (broken phone and poor code). The thing is that the old Android app could run 24/7 without barely impacting battery life.

Again, I see no good reason to keep the timer. If it was introduced to avoid people gaming the system, I hardly think that helps. Right now, with limited time, only very high intensity movement of the phone can result in max yield with the 2 hour timer. This is not possible when actually doing real sports! From my experience, running 1 hour makes around 1 mcz, mountainbiking 2 hours about 1.5 mcz. Putting your phone in the tumble dryer, helicoptering it in a sock etc makes more. If Mango really wants to target fitness and running, I think the timer should go and consider adding some sort of location tracking of distance/speed to leverage rewards to avoid gaming. Think about how Google fit and iOS equivalent runs in the background tracking activities. Mango can do the same (as the old app did). Also, getting rid of the timer and rewarding people who do long (and perhaps less intense) exercise might be an idea? In fact, my real favorite moments with Mango was going on 4-5 hour rides and getting larger rewards (possible due to cumulative cap and no time limit). Right now, the whole thing is more of a hassle and I will likely stop using it, and not to recommend it to someone else. Just a the opinion of a user, who has used the app for what it is targeting (exercise) since the beginning.