For those of you interested, this can be done in one day.
Leaving Merida at 7:30 AM, the LawsonMobile and it's guest left Merida for Chichen Itzá where we arrived just a few minutes after 9:00 which allowed for unhampered viewing of the ruins and crowd-less photography if one is interested in taking pictures without the herds of red-faced Cancun tourists. An additional plus is that the pesky vendors are still setting up shop and are not in your face with their not-typical trinkets like they are after 11 AM or so.
A couple of hours later, back towards Merida with a stop in Izamal and a visit to the convent/monastery/church. At this time, just after Easter, notice the 3 wooden crosses still standing where presumably there was an Acanceh-style ceremony depicting the last moments of Jesus Christ. Even though it was Semana Santa and supposedly there is a lot of Mexican tourism, Izamal was quiet and the horse-drawn carriages were lined up and waiting for something to do or someone to hire them. It occurred to me that these poor horses were awfully bored and had nothing to munch on, or even water to drink. Perhaps it might behoove (no pun intended) the owners of said beasts to have a bucket of water and one of oats so the animals have something to look forward to when they are standing around in the 100 degree (F) heat. As it is, they are on the hot pavement, staring alternately at the hot pavement and the back of the calesa in front of them.
FYI, this trip took about 6 hours and we were back in Merida, passing through a brush fire just outside of Izamal, by 2:00 PM.