It definitely takes time for your sit bones to adapt to the pressure of a harder saddle. But it's good that the pressure you're feeling is on your sit bones! It's where the pressure should be. You should adapt over the next week or so and as mentioned above, if you don't you may want to try a different saddle but I wouldn't give up on this one too easily because it sounds like you're sitting on the saddle in the right way and that can be hard to come by.