I think the best time for effective study would be Morning (4am -8am).

Reason for this is that Early morning is a time when there is very less movement of any form. You would be the only one awake in the house and there won't be anyone for distractions.

You will experience the coll morning breeze. I find it as a catalyst for rapid learning.

Waking up early doesn't have any adverse effects on health.

Hope it helps.