They can probably setup all the equipment right next to the DOCSIS 1 equipment, and then do "scheduled maintenance" for a few hours in the middle of the night to do the switch. Depending on available space, they may have to do equipment switchout in sections, and thus have a few outages.
They are usually planned in the middle of the night, often between 1 and 4 AM. it may affect you if you are a night owl, but 98% of people are probably asleep between those hours, so effect on data communications is limited.