Shalom Rabbi. Someone pointed out the fact that it is not good to sleep in early hours of nights. I dont know if that means 3 hours after Shkiah or 3 hours afterTzeit Hakochavim! Can you please guide me. Thank you.

According to Kabbala, it's better to sleep at the beginning (!) of the night, and then wake up at chatzot (midnight) to learn or say Tikun Chatzot. On the other hand, Rav Ovadia Yosef and others say that the custom today is to learn Torah at night until late, and that's what's accepted.