The answer, unfortunately, isn't really quantifiable without knowing a lot more about how one constituent route fails, where you're measuring from and how that given remote is connected.
First off - your question isn't really a function of being located in a particular country as much as the specific providers in use, their connections to one another and where you're testing from.
As an example - if both London and Japan have connections to the same carrier then there likely isn't a whole lot of reconvergence required beyond the AS boundary of that carrier and any delay is going to be due to the mechanism of the route disappearing (e.g. explicit retraction vs dead peer) and the subsequent propagation within the carrier's network (usually fairly quick).
If London and Japan are connected to two different carriers then convergence is going to be a function of the above (means of route removal) plus the particulars of how a given point sees the routes in question. This is going to vary quite a bit. Changes to the routing table may need to propagate through a single AS or through a half-dozen. Each AS could consist of two or three routers or a dozen.
TL;DR - It's hard to quantify this, as it will vary tremendously by how you're connected and from where you're measuring. Best-case is convergence in a few seconds, worst-case several minutes.