Power off first. The modem has enough power to tell the DSLAM it has lost power so it not be logged as a lost sync through noise or attenuation. Then remove the line cable.
On powering up, reboot the modem and allow to stabilise for a few minutes before connecting the line.
As for the time, I have never experimented but would expect there to be something similar to ADSL where rebooting a couple of hours after dawn gained the best sync but if I use an unlocked modem I can see the figures for sync and achievable changing continually. So, it appears not to matter - but no harm in trying an 8:00 or 9:00 reboot.
M H C
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