With 21 hours you can have the tour or hotel as I understand it (I've not done this but will be this week and think my research is sound). There is a dedicated thread on this with lots of good insight from the experts.

I have 18 hours one way and 10 the other and have opted for tours in both directions. I am hoping that I can grab a nap in the business class lounge before my tour; I have since learned that my outbound flight is frequently several hours late so my layover may be more like 24 hours so I am counting on business lounge amenities for the remaining time.