OP,
I am divorced and share custody and I don't think this is too long for the children. My DC was separated from me for 9 days at age three, shortly after we'd told DC about the separation, and was with dad and grandparents and was fine. Of course every child is different. (It will probably feel longer for you!)
What bothers me more is his flagrant disregard of your agreement. You've got 15 more years of this. It's sweet that you are concerned about the children, but I'm much, much more concerned about you. Especially reading that he was abusive in the past. Often the dynamic follows you post-divorce.
Flexibility is a two-way street. He wasn't being flexible here. He excluding you from the planning, on time that is yours with your children. That is a huge no-no. Do you want this to happen every spring or holiday break? What about summers? This isn't about going to court, it's about setting a precedent where he could -- could, I don't know how agreeable or disagreeable he is -- books flights at his convenience and if you protested tell you that you seemed okay with it one time, why not this time.
In my mind, you should get this straight now, and make clear that he should not book flights involving the children until you've finalized everything, including dates and makeup time if that makes sense. He could pull this again.
I'd write an email, along the lines of: (An email, not a text.)
In the future, please do not book flights for vacations -- in general, but especially if they depart from our agreement -- before discussing them with me. I know the children will have a great time with their grandparents in Florida. Given I'm missing XX days with them, I plan to make them up WHEN.
(It's important that he not book flights period without your input because your work schedule might mean some switchoffs, etc.)
Hang in there.