The answer is: establish a regular bedtime routine and consistently go through this routine before sending Billy to bed
Our body response strongly on habbit. When we establish a regular bedtime, our body would conditioned to be sleepy and ready to sleep that that particular time.
This make establishing regular bedtime become an effective tool for those who want to obtain enough sleep hours despite their busy schedule. Other things that beth can do to make the conditioning even more effective is to only make her bed time specifically for sleeping and do all her works on the other room.