I used this recipe a while back and it works. Apparently the idea is that the gelatin keeps the sugar locked away from yeast long enough to prolong the CO2 production. However, under normal room temperature, the jello mixture will melt into a sticky mess. I would get on average maybe 4 weeks of CO2. I'd just skip the jello and use champagne yeast and light brown sugar IMO.
The Fraternity of Dirt #112