Just join on 1 campaign then, why do you need to join in all campaigns while you can't handle it?
This seems to me to be the best answer if you cannot handle to join many social media bounty campaigns then do not do it, social media campaigns do not seem to pay as well and there is a huge amount of competition so the payment is reduced even further, so join a number of campaigns that feels natural for you once you have more free time you can join a larger number if you want.