My robo is up at 5pm-8pm, then 10pm-2am and up again at 5am-8am. He also comes out various times of the day but that's for food, drink etc. Roborovskis are crepuscular in the wild and that means they're awake dawn and dusk normally.
Syrians are normally nocturnal in the wild meaning they come out at night. Athena definitely follows that rule. I never see her throughout the day, I hear her, but don't see her. She normally gets up around 11pm and goes back to sleep around 6am.
Lilith is up all different times during the day and becomes really active at around 9pm but to be honest the whole nocturnal thing goes straight out the window for her. Most awake Syrian I've ever seen, and she's the oldest.
Ghost is normally up properly after 6pm but never goes on his wheel or makes any noise until I've gone to bed. Then it's a symphony of wheels and bottles.
They're all individuals and some take longer to settle in than others. As long as they're eating and drinking ok then I wouldn't be too worried