The third of the key missteps that we all do is - not setting a time limit for ourselves. Each search we do has a different value to us - which we often ignore. Sometimes we spend hours on a small matter and not nearly enough time on an important matter. Determine three things: 1) when is the information due; 2) how much time will allot to it; and 3) when will you spend the time searching. Only you can set these things since you know it or the person asking you for the information has told you.
Ask the librarian or friend who is helping you on the more difficult search to estimate how much time they think it will take. Librarians have done so many searches that this is not an unreasonable question. Also as if they think you will find the whole answer or only just part of it. We want to search efficiently and save time.