P7 on what exchange? you mentioned Wallington on another thread but P7 on Wallington isn't at capacity so I'd guess it's another exchange?
how long does this work take to carry out in general or no info really on how long.
That question seems to make the wrong assumption that they do this upgrade when a cabinet gets full.
I know a couple cabinets that have been full for over 2 years with no sign of expansion or a 2nd cabinet on the way.
Providing the exchange/cabinet number will allow some well connected members to lookup this info for you.
Be prepared to hear that there are no plans to add capacity as that's very likely.
As I mentioned earlier your port should already be allocated so you should be alright.