They had time to build a mock up of the compound and practice on it.While the mobile DNA lab is news to me and would explain how a DNA test is possible onboard an aircraft carrier I still have to question how quickly one could be processed (even your link gets vague in that aspect). The other is the fact that this raid was decided on in a 16 hour time frame - would a non essential piece of equipment be transported across several time zones and delivered to a carrier deck, set up and produce a DNA sample in 28 hours total?
My understanding is that the practices were over a period of 2 weeks.
14 days is plenty of time to plan for the contingency.