In my experience it has been 100% reliable since I started using it a few months ago… always matching my intelligent slots, no matter when they are (early evening, overnight, extended mornings etc), allowing my car and home battery to charge whenever the slots are made.
However, if you are attempting to make your car only charge during the “core hours” of 23.30 - 05.30 to be double sure, then you don’t really need to use this integration - though, you aren’t then taking advantage of Intelligent, nor allowing Octopus to attempt to flatten out demand levels.