I have applied for a student visa to be valid from September, 1st but since I have not yet got my student visa I will be in trouble to move to NZ in September, so I want to ask from Visa officer to issue my student visa at least 3 months later.

I have 2 questions, (My professor is OK to start my study in February, 2010):

1- If the student visa is issued for September,1st do I have 3 months thereafter to enter NZ?

2- If I want to enter to NZ late January, 2010 (instead of September,2009) which way is better:
a- Ignoring I have applied for September,1st and request to issue my visa for late January

b- I wait to issue my student visa for September and then I ask for an extended validation for 5 months instead of 3 months.