Dê uma olhada em man 5 crontab
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Note: The day of a command's execution can be specified by two fields — day of month, and day of week. If both fields are restricted (i.e., aren't *), the command will be run when either field matches the current time. For example, ''30 4 1,15 * 5'' would cause a command to be run at 4:30 am on the 1st and 15th of each month, plus every Friday. One can, however, achieve the desired result by adding a test to the command (see the last example in EXAMPLE CRON FILE below).
Assim, seus servidores devem reiniciar todos os dias de 15 a 21 E todas as terças-feiras.
Veja o exemplo das páginas de trabalho:
# Run on every second Saturday of the month
0 4 8-14 * * test $(date +%u) -eq 6 && echo "2nd Saturday"