Isso executará seu comando a cada minuto. É uma sintaxe válida.
Aqui estão os detalhes de info crontab
:
The first five fields shall be integer patterns that specify the
following:
1. Minute [0,59]
2. Hour [0,23]
3. Day of the month [1,31]
4. Month of the year [1,12]
5. Day of the week ([0,6] with 0=Sunday)
Each of these patterns can be either an asterisk (meaning all valid
values), an element, or a list of elements separated by commas. An ele‐
ment shall be either a number or two numbers separated by a hyphen
(meaning an inclusive range). The specification of days can be made by
two fields (day of the month and day of the week). If month, day of
month, and day of week are all asterisks, every day shall be matched.
If either the month or day of month is specified as an element or list,
but the day of week is an asterisk, the month and day of month fields
shall specify the days that match. If both month and day of month are
specified as an asterisk, but day of week is an element or list, then
only the specified days of the week match. Finally, if either the month
or day of month is specified as an element or list, and the day of week
is also specified as an element or list, then any day matching either
the month and day of month, or the day of week, shall be matched.
O artigo ao qual você está vinculado parece ser bom. Está dando alguns bons exemplos e é realmente mais fácil de ler do que o excerto de página de manual que forneci aqui.
Você deve ser capaz de usar a sintaxe que fala.
De acordo com o meu crontab, o @daily é executado às 6:25.
$ grep daily /etc/crontab
25 6 * * * root test -x /usr/sbin/anacron || ( cd / && run-parts --report /etc/cron.daily )