Instead of the first five fields, you can use any one of eight special strings. It will not just save your time but it will improve readability.

Special string    Meaning
@reboot ——> Run once, at startup.
@yearly ——> Run once a year, “0 0 1 1 *”.
@annually –> (same as @yearly)
@monthly —> Run once a month, “0 0 1 * *”.
@weekly —–> Run once a week, “0 0 * * 0″.
@daily ——–> Run once a day, “0 0 * * *”.
@midnight –> (same as @daily)
@hourly —–> Run once an hour, “0 * * * *”.

For e.g. run ntpdate every hour:
@hourly /path/to/ntpdatevim /etc/ssh/sshd_config