I've done this a few times before, LAS-LAX, LAX-LHR or LAX-AKL.

UA's system will not allow you to check luggage through or issue BP's on the NZ leg if you are somewhere less than 3 or 2 hours in connection the UA system. And there is absolutely nothing the checkin agent or supervisor can do about this, they can only check you through to LAX, you collect ur bags and then go over the NZ terminal.

I have done this with a 70 minute connection in LAX... can't believe bmi even allowed this to be issued, I have done the trek before and basically, i had my priority tags on my luggage and they were the first to come out, and then i bolted across to the NZ terminal (walked over rather than waiting for the bus, walking through the carpark in the middle) and NZ were still there to check me in, no probs. I checked in with 50 mins before departure. And still had 10 mins to grab some food in the NZ lounge before departing to LHR...

So it is possible especially with the time you have, you'll just have the difficulty of not being able to get your BP and check your bags through at your point of origination.