Extending a visa and booking boat tickets

Hi all. If I get a 30 day visa on arrival in Vanuatu, how long does it take to extend it to 6 weeks? Is it possible to do in one day?

Also, is it necessary to book seats in advance on the boat from Port Vila to Malekula / Santo? If so, how far in advance, how and where? Is it possible over the net?

Thanks!

Getting my extension took sg. like 10 minutes.