I ended up figuring it out after looking at many different places, maybe not the cleanest... 

for record in self:
	if record.x_studio_warranty_end:​
	​	​dt = datetime.datetime.now()
	​	​dwarr = record.x_studio_warranty_end
	​	​dwarrdt = datetime.datetime.combine(dwarr, datetime.datetime.min.time())
	​	record['x_studio_days_remaining_on_warranty'] = (dwarrdt - dt).days​