The timeline is roughly this:
Size 1, scenes 001-009 Early to Mid-Spring
Size 2, scenes 011-29 Mid-Spring to Summer
Size 3, scenes 030-49 Summer
Size 4, scenes 050-69 Fall
Size 5, scenes 70-89 Winter
Size 6, scenes 90-100 Late Winter to Early Spring
The specific start of the various sizes depends on the route, but this is the approximate framework for all of them. The time elapsed between subsequent scenes can vary from hours or the next day to possibly a full week, so they can't be pinned down to a specific calendar date (unless it is a holiday or a character's birthday).
If you're curious about the lore and more meta aspects of the game, we always encourage people to join the discord server where these types of questions and discussions are discussed with fellow fans and the development team . https://discord.gg/rgBEwRG6