The Season Pass for Dying Light consists of the following items:
In addition, Season Pass owners have access to the upcoming expansion, The Following.
Having said that, Season Pass is just a name - not a DLC itself, while its owners have the above items installed on their systems regardless of whether the Season Pass checkbox is ticked or not. To conclude - no worries and enjoy the DLC's!
The release dates of The Following for a given region and platform are as follows: