Believe it or not, the maximum speed limit in the whole country is 80 km/h. In Port Vila, the limit is 50 km/h and in some of the villages, even less. However, there are no radars, speed cameras, speed traps or even pursuit vehicles - but any big bike is easily recognised. The ring road is about 160 km so if there are no stops, a bit over two and a half hours if you stick to the limits.
A TT? Perhaps with Stelvios or equivalent - but you'd need a lot of people to ensure the pigs and dogs stayed off the road.