Camille, how fast can your course be completed?

I saw your first day video, and I am thinking about buying your entire course. It is a 4 week long course, but I notice that the videos are split up in days, so day 1, day 2 etc. I wonder if I can complete the course faster than 30 days? If you had to give an estimation, what speed could I go through this course without losing any quality or risking injury? Can I watch two videos a day? Three? 

As you said in your first video, there is no advantage in rushing through. But I just wonder what speed is fast without counting as rushing through. 

That's really up to the level you're currently at and how your voice is feeling! Many of the concepts covered will take a while to "sink in" and become muscle memory, regardless of the speed. You could feasibly watch 2-3 lessons per day and familiarize yourself with the concepts, but that won't allow for much practice time. Think of singing as any other physical skill: you can watch 30 videos on perfecting your jump shot in one day, but you'll get much better results by watching one video, implementing what you learn in your practice, and moving on when you're ready.

You can read this article for advice on how to get the most out of the course: https://www.30daysinger.com/blog/one-lesson-per-day-how-to-practice-for-the-best-results.