Also don't forget to go on the promenade for at least one lock. you will see and almost be able to touch the walls. 100 years of engineering working exactly as engineered.
Also please remember it is Panama Hot! Water and shade!
As stated above it is a full day and you will be going through the old locks. Enjoy and see it from many viewpoints. Walk about, have a nice lunch while on Lake Gatun. Remember this; the islands you see are mountaintops before it was a lake.
Cheers