Geography is a subject which needs huge coverage. But 5 months is too much for one subject considering that there are another 6 to seven subjects namely history,polity,science,economics, ethics and aptitude,environmental studies and optionals. I would recommend you to allot 1 and half month for each subject inclusive of daily current affairs coverage. News paper takes not less than 3 hours. So you may allot another 3 to 4 hours for 1 and half month. That should be more than enough.
Books for Geography
11 th and 12th ncert books compulsory as they have very important topics. They provide basics which is quintesse
Certificate of Physical and human geography by G C Leong is a must book for both prelims and mains
For world geography again I would like to recommend GC Leong and pick important topics from internet.
Along with a map based study will enrich your knowledge .For that I recommend The Orient blackswan Atlas/Oxford atlas . Here is the Full list of Books for Prelims and Mains Exam . If you are a Hindi Medium Aspirant Check this link : List of useful UPSC Books in Hindi Medium .
Time I have recommended may not be sufficient,but you don’t have other options because of limited time for UPSC. Know what has not to be studied and do not spend time on those topics. And remember smart work is all that is required in UPSC.. Good luck..