I would not recommend the Palace of Versailles due to the fact that it was so over crowded, to the point where you couldn't enjoy the whole experience. Plus I visited the Palace many years ago and it was beautiful. Now it's run down inside so disapointing and they have added structures to the outer part that it took away the whole old world palace look. Save your money and just take out door pics.
Thanks to Nicola our driver who had taken us there and back to Versailles. She provided an excellent historical talk relating to the Palace. The Palace and gardens are a must. However I think another hour in the gardens would have been perfect.
So I think at least 3hrs to see the Palace and Gardens which are a treat to the eye.
The guide was terrific - she prepared us well, made sure we stayed together, etc., very congenial etc. However Versailles itself was so dang crowded. We missed some rooms due to them being packed with people. The best part of arranging this via Viator was everything was taken care of - I would never attempt to see Versailles or the Louvre without a guide. Thanks!