That leaves five nights/four days to visit Chichen Itza and Merida - we'll be using public transport.
I'm thinking along the lines of:
Sat: travel by bus Akumal/Cancun/Merida
Sun: day in Merida
Mon: day in Merida
Tues: travel to Chichen Itza
Wed: visit Chichen Itza
Thurs: bus to Cancun airport
or we do it in reverse; when is it best to visit the ruins, weekend or weekday?
I think from reading the forum that it might be best to be in Merida at the weekend.
So will we need to book a hotel in advance in Merida and if so, can you recommend any (mid-price) where we won't need a car?