After sending a project proposal, you should wait for an answer.
For me, I would wait for 3-4 days(at least), just to give them time to go through and understand. They may not be just sitting to receive my proposal(and have other priority work as well). So, I would choose "True" which is actually wrong according to you. So, I would send reminder after 3-4 days or may be after 5-7 days( depending on the culture of the company as well). That is how personally I feel.
Maybe in this case you have misinterpreted the question. "Waiting for an answer" means to do nothing until the potential customer answers, and your thinking is exactly the opposite to that: wait only an amount of time to not seem annoying and contact them, corresponding to the "False"answer.
However please note that we will improve the question to avoid this ambiguity.