Next winter I would like to go to Central or South America. I'm already looking for some possible itineraries for approximately 3 or 4 weeks. I found La Ruta Maya which sounds pretty interesting. Can this journey be traveled in 3 weeks without skipping too much interesting stuff?
I did a few searches. This UK travel company has a 15-day itinerary. This regional summary has 7 stops each for a day or two with some possible side trips. So it certainly seems reasonable that you could create your own route and spend a very enjoyable 21 days.