When we were there last month, has it been a month already, The story telling started at 7:30, roughly. Lasted for about 30 minutes but there is no script so length depends on who is telling the story. You could call AKL and ask what time the story telling takes place so you can make PS's. If that doesn't work I would make PS's for 8:30 or 9:00.
Head back to Arushu rock after dinner and ask the CM there to use the night vision goggles.
Have fun and beware of the toads...lots of toads come out after dusk.