@Panhandle Couple, the 3 hours in Colon is standard for partial transits, and it mostly for picking up people who got off the ship in Gatun Lake for excursions. It is NOT a stop for the purpose of doing an excursion from Colon. Given the time it takes to lock up to Gatun Lake, tender excursions ashore, then seek a slot to lock down again, there is rarely much more time to dock at Colon.
When you schedule 10 day cruises, usually one departure is on a weekend day, the next will be a week day, followed by a weekend day, etc.