As soon as.
Just don't reboot or disconnect the modem
until after the end of the second day, including the day of connection. That's if it is connected for more than 15 minutes in the first day. If it is connected for less than 15 minutes in the first day then don't mess until after the end of the third day.
Unplugging the HH from it and connecting your own is fine, right from the start.
My broadband basic info/help site - www.robertos.me.uk
My domains,website and mail hosting - Tsohost
. Internet connection -
Plusnet Value Fibre
"Where talent is a dwarf, self-esteem is a giant."
- Jean-Antoine Petit-Senn.