Time-to-reimplement is not and should not be a measure of patent validity, because a patent isn't about difficulty of writing the implementation, it's about the cleverness of the solution. What needs to be measured is "given the same problem and existing tools but no knowledge of this solution, how long does it take to come up with this idea". A clever solution that takes 20 minutes to implement but that nobody would think of in a dozen years should be patentable while a solution that takes months to implement but seconds to imagine shouldn't be patentable (but is copyrightable).

In this case though, I'm not sure "we took a first-party API and applied it like other products, but we used dimming instead of highlighting" qualifies.