One thing that is rarely done in model plane design is to test the instructions. It’s quite surprising what can be learned about a building method when QA or user testing is run on an instruction sheet.
This was done on the Squirrel (about 40h worth for the current version of the instructions).
The idea is to get some people that have never seen the Squirrel project (and don’t build model planes). You sit them down in a comfortable environment to make a Squirrel. Do not tell them they are testing the instructions. Tell them that the purpose of the experiment is to determine the correct length of time that should be alloted for this exercise.
You cannot help them but it’s okay to consult other people that are not model plane builders and don’t know the Squirrel project. You observe them and take notes on any mistakes they make. Also note any steps that take them very long. Later you make revisions and run the test again. Issues that come up for multiple people are more serious than issues that only one person cannot solve.