You may find that you study best in ten-minute bursts scattered throughout the day. Maybe you prefer two 25-minute sessions with a short break between. You may work better in the morning, in the evening or somewhere in between. Whichever suits you is the one to choose.
Tip: Try setting a timer and see what happens if you try to concentrate for 10 minutes, 20 minutes and 40 minutes. Try several permutations and see what works best for you – then stick to those limits.