I am curious....does the tour say it is about ten hours total? Or ten hours from arriving at Versailles to leaving Giverny? If the former, after factoring in travel times, and waiting in the security line at Versailles, it seems to me you are getting a very limited amount of time there. Monet's house and gardens can be seen in about an hour, although somewhat rushed, if so, but two hours there would be much better. If you can visit these two places on separate days, it would be much better, as Versailles is huge. Even if you don't see a lot of the grounds, the palace can take quite some time to explore. You would not be trying to rush through Versailles (hard to do) if you allow most of the day there. Giverny would be a good half day due to the distance from Paris.
Just a thought. Of course, you must use your time in Paris in a way that best serves your wants and needs there. Whatever you decide, Paris is always wonderful! Amusez-vous bien!