If you find that your cronjobs are not launched at the specified time, chances are it's a timezone issue.
The timezone of cron is specified in /etc/timezone, according to cron's man page:
The daemon will use, if present, the definition from /etc/timezone for the timezone.
If you change the timezone of the machine but has NOT restart cron, cron will still use the old timezone. In order to make your timezone effective, restart cron sudo service cron restart.