Time prepositions in Tagalog grammar are used to express when something happened. They can help instantiate the time of an event, whether it has happened, is happening, or will happen. Some important time prepositions in Tagalog include ‘sa’ for ‘at’, ‘bago’ for ‘before’, ‘habang’ for ‘while’, ‘simula’ for ‘since’, and ‘hanggang’ for ‘until’.