"I think it can be discouraging to some when maybe you zap a really good post early on a day where zapping ends up not being rewarded, or maybe you make a really great comment on a day where early zapping is rewarded, instead."

Generally speaking you should not aim at getting paid but aim at gaining knowledge. The rewards should be irrelevant. If you think about rewards more than about the actual topic you're already compromised no? Your thinking should be independent from monetary incentives.