If you're really stuck with this requirement, and vixie cron is your only tool: */1 * * * * /usr/bin/bash -c '[[ $(( $(/usr/bin/date +%s) % 6000)) -eq 0 ]]

If you're really stuck with this requirement, and vixie cron is your only tool: */1 * * * * /usr/bin/bash -c '[[ $(( $(/usr/bin/date +%s) % 6000)) -eq 0 ]] && mycommand'