I prefer to take this route to Christchurch  easier road. Stop at Kaikoura and see the whales. Excellent boat tour, or if the sea is rough, take a helicopter ride. Whales and dolphins are there all year.

Hammer Springs is a nice area to visit also. Some lovely small inns in the valley. Take a mineral springs soak. Amazing walking trails in the area.

You can take the train at 1.p.m. which meets the ferry from the North Island, and arrive in Christchurch at 6.30 p.m. if you dont want to drive.