https://man7.org/linux/man-pages/man1/at.1p.html
En itt nem latom a masodperc pontossagot.
Ahogy termeszetesen itt sem:
https://pubs.opengroup.org/onlinepubs/9699919799/utilities/at.html
A BSD at-nak van egy jo kis implementacios reszlete:
IMPLEMENTATION NOTES Note that at is implemented through the cron(8) daemon by calling atrun(8) every five minutes. This implies that the granularity of at might not be optimal for every deployment. If a finer granularity is desired, the /etc/cron.d/at file can be edited and will be read by the system crontab, from which the SHELL and PATH environment variables are inherited.