Through research it seems like travel times are a lot longer than estimates even given on newzealand.com.

We fly from Nelson to Christchurch and spend 1 night in Christchurch, then we will be driving to Twizel for the next night.

Would trying to add in driving from Christchurch in the morning to Castle Hill be too ambitious? I'm hearing it takes about 5-6 hours to drive from Christchurch to Twizel with a stop or 2 on the way.

If so, would picking up our rental car and driving to Castle Hill the day we arrive in Christchurch and back for the night be too much?

thanks