Moving from ADSL to FTTC and changing ISP - downtime?

Does anyone know what the likely downtime would be when changing from ADSL to FTTC and changing providers at the same time?

Would it be similar to when just changing providers on ADSL or FTTC - i.e. no real downtime, just the router swap or updating crednetials in the router on a designated day?

Maybe 20 minutes or so whilst the cab jumpers and testing are carried out.

Thank you.

It can depend on who you are moving to - I am pretty sure people moving to PlusNet have had issues where the move has happened but PlusNet haven't enabled the account as they may only do that after OpenReach have informed them the move is live so could be the end of the day before it happens. Don't know if this happens at any other ISPs.

I know your original question is regarding downtime, but when I did a combined ISP move and ADSL upgrade to VDSL a few years back - although the ISP said it could happen in one go they could actually only do an ISP takeover on ADSL, wait for that to complete before they put in a VDSL upgrade.

Not sure if this is still the case.