the rewards are not great but i think they are worth doing. there are a couple random drops while doing the quest and the quitisential fruit and wings at the end. there is also a trade-in drop that is random everyday which has had decent payoff, at least for the 1-500 quest. i do not know if the 500+ get better rewards or not. and to answer your question grimbly, as long as you renenerate 8 energy every 5 min, less than 12 hours will be needed to accumulate the required 1100/1130 energy needed for the quest. for all low levels a daily boost of 20 or so att and/or defense is imensly beneficial and the wings help you do the quest more easily.
the quest does not have to be done in one day either, there is just a maximum of 101(?) times for the reward. doing it 50 times one day and 50 times the next will still be as good a place to spend your energy as any. the quest will not level you up as some wish but it will make anyone who tries it much stronger for doing so
and i'll put in a side note as well. that is a very big jump from 500-501. a level 490 will most likely get way more out of the quest than every level 510