I am going to suggets do not do it through the online form.
I did this a few months ago - about a week out from moving. At no point in the process did it ask when I needed the connection established. I phoned up to enquire and they said once it is in the system they cannot stop it.
They dropped my connection at my current address and connected at the place I didn't even have keys for yet. Without internet for a week while moving. Hopefully they took onboard my scathing feedback and fixed it.
