day trip to yasur

hi i have booked 10 days in port vila for myself and my boyfriend, staying at the melanesian. we can only afford to do a day trip to tanna to see yasur, and was wondering about peoples past experiences with united airlines and their tours? i have read suggestions to stay overnight on tanna, but it just isnt in the cards for this trip. if anyone could relay their experiences with united etc that'd b great!!

thanks

kirst