1/ It's not an error, only a warning. Unzip tries to set the timestamp on the file according to the content of the zip file and fails at that. The file should neverthelss be uncompressed. There are options to disable the time-stamping, but that only fixes the warning, not the real problem.
2/ You didn't answer TBOne's question: from which environment are you calling the script? From a simple terminal window? From cron?... Can you get the script
to print out it's environment, eg
env > script_env.txt
and then post script_env.txt's contents?
3/ What type of filesystem is the target directory located on? I'm thinking maybe the filesystem doesn't support the usual time-stamping done by unzip.
df -h /your/target/folder
of course replacing /your/target/folder with the right path.