No, the maximum is 180°
For this kind of cases, you should use a "circumvent angle" (see documentation page 220).
For instance, let's say you want to route from Caligliari to Capos Marco (even more difficult), then you should first create a routing to somewhere in the South (you can choose North if you want to turn on the other side) and count roughly the number of isochrons needed. This does not need at all to be precise. He we have roughly 20 isochrons
Then with this info, you can create the final routing, with -90° as a circumvent angle for 20 isochrons (note that in that case you also need to uncheck autozoom so qtVlm "sees" all.