Parasitic, but probably like mosquitoes or leech to us (outside being disease vector). Although they’re sucking its blood, Nue is too big to care and they don’t kill their food tank.
For setting the clock...
Going to assume they want to prioritise safe escape from all the crews. They want enough time for the B team to also evacuate the area into safety. It’s not funny if they fail to escape and Nue starts throwing its body in pain from one set of bomb. Or worse, can’t escape far enough when the nukes explode.
They also would rather not use the nukes, and for that the calculation say they need the conventional loads from two teams at minimum. Thus they wait so they can set it together.