In the books, the timeline is more unclear, but it seems more recent:
- We know that Mance was still with the Night’s Watch when LC Qorgyle visited Winterfell, and we know Qorgyle died sometime in 287/288. During the visit Jon and Robb were old enough to build a snow mountain on top of a gate as a prank, and Jon was old enough to remember Mance promising. Since Jon was born in 284 and Robb in 283, it is unlikely that it was much before 287/288, and even that’s pushing it slightly.
- Also, Osha says that Mance has never tasted winter, and we know that the current summer started in 288 AC, Mance had to have joined the Free Folk sometime after 287 AC.