Figure 1: crontab fields

minutes			-  can contain values  in  the range 0 through 59.
hours			-  can contain values  in  the range 0 through 23.
day-of-month		-  can contain values in the range 1 through 31.
month			-  can contain values in the range 1 through 12.
day-of-week		-  can contain values in the range  0  through 6.
Sunday is day 0 in this scheme of things.
For backward compatibility, with older systems,
unday may also be specified as day 7.
command			-  specifies the name of the command to be run.
A  percent  character  in this field (unless
escaped by \) is translated to a newline
character.  Only  the first  line (up to a % or
end of line) of the command field is executed by
the shell. The other lines are made available to
the command as standard input.
A field may contain an asterisk (*), which will always match the current date or time.