Answers:
 我会说:用 , (逗号)。从 man 5 crontab: 
Lists are allowed.
A list is a set of numbers  (or  ranges)  separated  by  commas.
Examples:  "1,2,5,9","0-4,8-12".
但是你的情况稍微复杂一点,你可以利用这个功能:
Note: The day of  a command's execution can be specified by two fields day
of month, and day of week. If both fields are restricted (i.e., aren't *),
the command will be run when either  field matches the current time.
For example, "30  4  1,15  *  5" would cause a command to be run at 4:30 am
on the 1st and 15th of each month, plus every Friday.
 所以在你的情况下,你可以写 0 9-5 8 * 1-5。这将在每个月的8号和周一到周五的每一天执行命令。 
 另一种解决方案是使用a test ( man bash,部分条件表达,和 man date ): 
# Run on every second Saturday of the month:
   0 4 8-14 * *    test $(date +%u) -eq 6 && echo "2nd Saturday"