Crontab has not to be restarted. Especially if you edit your crontob with the command crontab -e
.
Here the lines from man:
Additionally, cron checks each minute to see if its spool directory's modtime (or the modtime on the /etc/crontab file)
has changed, and if it has, cron will then examine the modtime on all crontabs files and reload those which have changed.
Thus cron need not be restarted whenever a crontab file is modified. Note that the crontab(1) command updates the modtime
of the spool directory whenever it changes a crontab.
It is strange that a restart of the cron service solved your problem. Maybe you solved some other possible problems as missing permissions.
You can add the user (e.g. root) behind the time format sequence who should execute the command/script. Then this user should granted the permissions to execute the given command.
Important: The last line of the cron-file has to be an empty line or a comment line!