I used MiniZinc on the capacitated vehicle routing problem in a combinatorial optimization project course a couple of years ago, and really enjoyed it.

The sweet spot for MiniZinc is in investigating a problem and prototyping a solution. I would say it takes 10-20 hours to get a workable understanding of the language and paradigm, plus or minus your previous experience.

However, MiniZinc is built on backtracking, which scales poorly to real world instances of np-hard problems.