Okay all that is mentioned, when Snape requests Dumbledore hide the Potters, is that it is fairly windy. That could really be any time, but it leads me to believe fall-into-Winter.
So that means the fall right after Harry was born OR the fall right before they were killed.
And matching it with the letter, where they were already under it for Harry’s first birthday… It would go
- July - Harry is born
- August/September - The prophecy / Snape telling Dumbledore/decisions on Secret Keepers
- October - Charm is cast
- Jan / Feb / March / April / May / June
- July - Harry’s first birthday, the letter. Sirius and Peter are still in hiding as well, or at least secretive and working with the Order
- Aug / Sept - Death Eaters or other people find Peter and convince him to turn sides?
- October - Peter betrays the Potters to Voldemort/underlings. The Potters die on Halloween