These three prepositions can be used to depict both time and position.
IN : Can be used to show general locations like neighbourhoods, cities, countries and places with a boundary. Ex: I live in India.
ON : Can be used to refer to more specific locations like streets, avenues, islands, surfaces and large vehicles. Ex: Latha stays on the fourth floor.
AT : Can be used to refer to very specific locations. Ex: You can find us at the park.