When should I use 'in', 'on' and 'at' for time and place?

There is a neat pattern. For time, use 'at' for exact clock times and short moments (at 5 pm, at noon, at night), 'on' for days and dates (on Monday, on 15 August), and 'in' for longer periods like months, years, seasons and parts of the day (in July, in 2026, in summer, in the morning). For place, use 'at' for a specific point (at the gate, at school), 'on' for a surface (on the table, on the wall), and 'in' for an enclosed space or area (in the room, in Mumbai). So your examples should be 'on Monday', 'in July' and 'in the morning'. A handy memory aid: 'at' is the smallest and most specific, 'in' is the largest and most general, and 'on' sits in between.