CX873 is long enough for you to enjoy the entire meal service after takeoff and still have lots of time to sleep. No need to opt for the light meal option unless you like what's on offer or really want to get ~10-11 hours of sleep.
I personally try to wake up just as breakfast service is starting. Or better still, slightly after it's started, have everything at one go, and change for landing. It's not exciting enough to sacrifice sleep for, especially since you'll be having one or two more breakfasts in the lounge and the onward flight!
If you wake up too early you might have a tough time pulling through the day.