It Started With a Kidnapped Pig...
The Forgotten Realms runs on the Calendar of Harptos. There are 12 months, and 30 days per month. Some months have a Holy Day of rest between them.
The year that this adventure starts is in the Year of the Scarlet Witch 1491 DR (see here about the names of years). The date the adventurers met as a combined group was 1st Mirtul (fifth month of the year, two weeks into Spring). They arrived in Red Larch on 3rd Mirtul. See Journal which details the party’s activities relative to the date.
Below is another calendar which shows when the seasons change.