I'm not quite sure what you mean that they are done at the same time? They would logically be very close to an hour apart, right?
The value of getting a +10 or +11, which would be 1 or 2 hours before the next shot, is that it tells you if the cat's BG is really going up or not. When this is really helpful is if you get a low reading when you are just ready to shoot. If you're questioning whether you should shoot that low number, it helps give you confidence to shoot if you have that +10 or 11 and know that the BG is already going up from comparing it to the last test.
It's not something you always need to get, but it can be helpful. If you have gotten enough to see that they're usually about the same, then maybe you don't need to get that late-cycle test as often unless you're seeing an overall lower cycle and you're worried about the next shot.