In my opinion, more or less the reward actually does not depend on the time of the bounty program, it depends on the quality of the project, the funds from the investor. In other words, if a bounty program is short but has called for the funds to hit their hard cap, it is actually better than a long bounty program. Therefore, I personally prefer a shorter bounty program.
The quality matters a lot but in this case i will try to remind you if the total staktes in the campaign will also determine how much you will get that dude. AFAIk if the quality of project will determine the price of token too and this will be determining how much we will earn from our work. Long term bounty program means it doesn't get enough demand.