as su, add crontab entries to call ifup and ifdown:
("crontab -e" to edit crontab)
* 22 * * * ifdown eth<X>
* 6 * * * ifup eth<X>
where <X> is your ethernet interface.
* 22 * * * ifdown eth<X>
* 6 * * * ifup eth<X>
where <X> is your ethernet interface.
# m h dom mon dow command
* 22 * * * ifdown eth0
* 6 * * * ifup eth0