I've been looking for work for 3 months now, while I do have some weakness I do have a set of technologies that is rare. I tried to give many exercises test but this one is different.

The potential company wants me to spend the whole day with them and from the interview, it seems they are going to keep me a whole day to work on a project.

My question is: How do I know to set a boundary of what I can do for free and in a 7 hours long day?