Well, you would be expecting the AM Lantus to be finishing up in the evening........yes, its meant to keep going to 9am the next morning, but in reality it wont be....it wont be very strong anyway....
You should follow your doctors advice, but I personally, would be tempted to take the new dose just before bed.....then the next night you can bring it back to 9pm....
you could also knock a few units off your evening meal so that you are going to bed and overnight just a tad higher than normal...