Perhaps we have different definitions of side project. As John H noted, this would be 15-20 hours outside your current job, nights, weekends, whatever.

This would assume you've gotten through an interview or two and both sides (employer and employee), want to move forward.

As a side note, if you didn't think this was a good idea, an explanation of why, or some reasons make sense. Jumping to conclusions and saying something is ridiculous doesn't seem like a thoughtful reaction.