I can't make myself due to external affairs to attend in town... But I could sugest/recommend Neil forks hut.
It would be a 6-7 hour day but it's a very nice hut by the river... I would try a swim there... It was too cold last time... :D
Too much...
Well, Sayer hut is another nice spot 3 hours away from Mangatarere road end.
Too short...
Renata is another option coming from Otaki forks. It's around 4-5 hours to the hut and another 20 minutes to the open tops with a really nice view of the valley.
All those less than around an hour driving apart from Sayer which requires crossing Rimutaka hills.
:)
MM.