If you know that you sleep at 12 midnight, wake up at 6.30am, and cannot study until 10am, so be it. There is nothing wrong in it. We are not machines that we automatically switch on our "Reading mode" the moment we wake up. But the smart thing to do is to your preparation according to your sleeping schedule. Might sound strange but that actually works. Be specific what you want to study within the hours that you are awake. Sketch a timetable and stick to it during the hours you are awake. If you think too much of preparation scares you or distracts you, divide the information to small and manageable parts. Let's say Mathematics is a more demanding subject for you, prepare for it when you think you feel the most active as in after your breakfast or cup of tea. Watch what you eat or drink because tea and coffee might keep you alert but iin the long run, they might cause anxiety, headaches and dizziness when taken in higher doses. And if you have less concentration span and if you think you more of tend to day dream, take frequent breaks. If you think you can only study for 30minutes at a stretch, do that and after every half an hour, take a 5-10 minutes break. And on those days that you think concentration is difficult, plan a mock test. Frequent review of material is important. And always make sure that you practise those formula or theories within 24 hours of learning them. You are more likely to remember things when you are willing to read and not when you force yourself to read. When you read something, find everyday examples of that theory or formula or information to make it relatable and relevant. Come up with what you have learnt in your own words. That way even if you start studying a little late, it is effective and doesn't go over the top of your brain.