The time requirement doesn't just set a limit for the candidate though, it also serves as a limit to consider for the interviewer when speccing out the project.

The time requirement doesn't just set a limit for the candidate though, it also serves as a limit to consider for the interviewer when speccing out the project. Having a time limit of a day or two is fine if the actual project should reasonably take a couple of hours, but if the project actually takes more than a whole work day to complete, then that's a different story (in my humble opinion, anything that would take more than a couple of hours is an unreasonable demand on the candidates time unless you offer some kind of compensation).