how to make a cron job run for once in a day code example

Example 1: how to run a script in crontab every day

30 2 * * * /your/command
# ^  ^
# |   hour
# minute

Example 2: how to run a script in crontab every day

+---------------- minute (0 - 59)
 |  +------------- hour (0 - 23)
 |  |  +---------- day of month (1 - 31)
 |  |  |  +------- month (1 - 12)
 |  |  |  |  +---- day of week (0 - 6) (Sunday=0 or 7)
 |  |  |  |  |
 *  *  *  *  *  command to be executed