If you wanted the task to run every day at 3:17pm, you would use:
17 15 * * * root newmail.sh
This says "run newmail.sh as root every day of the week, every day of the month, every month at 3:17pm."
minute hour dom month dow user cmd
minute - This controls what minute of the hour the command will run on, and is between '0' and '59'
hour - This controls what hour the command will run on, and is specified in the 24 hour clock, values must be between 0 and 23 (0 is midnight)
dom - This is the Day of Month, that you want the command run on, e.g. to run a command on the 19th of each month, the dom would be 19.
month This is the month a specified command will run on, it may be specified numerically (0-12), or as the name of the month (e.g. May)
dow - This is the Day of Week that you want a command to be run on, it can also be numeric (0-7) or as the name of the day (e.g. sun).
user - This is the user who runs the command.
cmd - This is the command that you want run. This field may contain multiple words or spaces.