I completed my VI on 23/12 and only heard back from them on 27/01 - so way more than a month! I think in their case no news is good news, as they're still reviewing applications. Plus, I think their AC's run into March so you can still be invited to those dates if you haven't heard anything yet. (This is re the London office).
I mean, that would be great if so! Since I haven't even been invited to VI though I have a bad feeling about my case.