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.