For SQ12 I stay awake for the entire SIN-NRT sector and try and sleep after the dinner service is completed on NRT-LAX. This way I wake up 2hrs before arrival (roughly 10:30~11AM LAX time).
SQ1 SFO-HKG is a long flight, I try and stay awake for the first few hours and sleep until the pre-arrival meal for HKG. If I sleep to early on this sector and stay wide awake for HKG-SIN I end up tired in the early afternoon in Singapore.
Enjoy your trip!