If the flats (as a block) are already served, and all landlord permissions have already been granted, then it could be a quick job with no hassle - a couple of holes drilled, connected up to existing infrastructure, and you're good to go within the quoted timescale.
If that's not the case, then the installation may take months whilst landlord permissions are sought, and even then there's a chance that the installation will never happen if VM can't get easy access to service ducts within the flats, or if VM decide that the costs of installing exceed the standard budget they allow for new connections. The chances of getting up to date, reliable information on the progress of the installation are very low indeed - if there are delays or problems, the only thing you'll see is your installation date getting pushed back, without explanation, and with the next date being no more dependable than the first.
If you cancel an existing ISP on the basis of a promised VM installation date, then you may find that you're left without any service.
