All I know about Vance is, when studs came back for Helo Advanced in Whiting, there was a marked amount of deprogramming that had to take place early-on. Kids had to learn the Navy way, and were given a few opportunities (sitting in on CPT's) to adjust before moving on in the syllabus.
I would say that more often than not, it's on a case by case basis whether this occurs. When I showed up to Corpus for advanced, we didn't start flying until a couple of months after ground school started. During that time, I got gouged up by the other Navy and Marines studs on what I should expect to know and prepare for flights. After ground school we had CPT's which further helped me prepare. By the time I got to the flights, you couldn't tell whether I had gone through AF or Navy primary.
As to whether someone should volunteer or not? It depends. I'll tell you how it worked out to my advantage. Going into API, I was at the tail end of my peers, simply due to the fact that many of my peers already had PPL's and did not have to go through IFS. At the completion of primary, I was now ahead of most of my peers. The scheduled end date at Vance is when you MUST be done, that's simply how they do it. If you get behind due to weather, you will start to fly weekends and fly doubles during the week. You may even sim up to the next block. Either way they will get you done.
Whereas in Navy training, weather delays, aircraft down to maintenance, these things will keep pushing your end date further and further.
One last thought, those mando 12 hour days, I'm pretty sure mine lasted for AT LEAST 2 months. And if your flight starts sucking on tests or checkrides, they WILL bring back those 12 hour days until your flight fixes itself. At least that was my case.