A crontab file has five fields for specifying day , date and time followed by the command to be run at that interval.
* * * * * command to be executed
- - - - -
| | | | |
| | | | +----- day of week (0 - 6) (Sunday=0)
| | | +------- month (1 - 12)
| | +--------- day of month (1 - 31)
| +----------- hour (0 - 23)
+------------- min (0 - 59)
* in the value field above means all legal values as in braces for that column.
You could use 0 1,13 * * * which means for every 1AM and 1PM.
0 1,13 * * * rm /var/www/*/somedir/index.php > /home/someuser/cronlogs/some.log 2>&1
where * can be replaced by different domain names.