1. Redirect the standard error and standard out to a file to see for any possible error.
Modify your crontab entry to
23 30 * * 1,3,5 /usr/local/bin/script >> /tmp/script.out 2>&1
2. This script will execute @ 11:30 PM on mon, wed, fri. I hope you are checking the result after this only
3. It is a good practice to use absolute path to commands specially when the script is expected to be run via crond