Working on my script

Am about to start my videoing of users viewing the three sites I have chosen.
The script is written but am unsure how long I should make this being they are friends doing this and there is no monetary incentive, probably a liquid one. I trialed it on my daughter who failed miserably but then the sites are very business orientated and she is only 12. When I say failed she did not understand the business terms used for half of what I was asking her to do.
Which got me thinking about the audience you are pitching your site to, you never really know who will visit, it could be kids doing a school project in which case only one of the sites I have is kid friendly. The other problem can just be the internet experience of the user so they miss things that while obvious to an experienced user may not be to them - the logo being the home key comes to mind, or the assumption that you will recognise the web address as home.
The exercise was useful for working the bugs out with the video and sound recording. Now on to the real thing...