Hi, which word should I use, in or on, a specific date? eg. should I say I go to work on July 7th, ? or use in?. If you're an English language learner, it's important that you learn how to use prepositions of time and date. Here are explanations for each of. We use: AT for a precise time [AT 3pm, AT noon]; IN for months, years, centuries, long periods [IN , IN the summer]; ON for days and dates [ON Sunday, ON.