2 months ago, When enable came door knocking, I accepted Fibre installed. It was a basic install and I am very pleased with the work done. Was told after the job was done to contact any RSP / ISP when I am ready to use it with a suggestion to do it asap. I assume its so enable can make money from the install? Rather than that they will turn my VDSL off.

Anyways I am currently on 2degrees naked VDSL 110/44 with no problems. 

I have a spare Fritzbox 7490. The GPON Light is on huawei ONT is working with a ethernet cable ready to plug into the fritzbox.

My question is there any downtime if I make the call to switch to fibre? Will there be a overlap where VDSL and fibre can be working at the same time ?

The reason I delayed is because I cant afford any prolonged downtime. So I  stayed with VDSL.