Oncycle PE Reference Checks

Have a few questions regarding the reference checks that seem to be something everyone used to go through as part of the PE recruiting process:

1. Given how early oncycle will likely be this year, I might still be in my training program or maybe 1-2 weeks onto the desk by the time they perform reference checks. In such cases, I won't be able to know anyone well enough to put them down as references, and I imagine anyone from my group that gets called up as a reference wouldn't know me well enough to provide any useful comments. How will the reference checks work given this early timeline?

2. I read somewhere that the oncycle process will be extremely quick and people could get offers right after their superday. However, I've also heard that reference check process typically occur after the final round and before they officially extend an offer. I imagine that these two cannot be true at the same time, so what actually happens? Or is the reference check process different now given the early oncycle timeline?

3. How long do reference calls usually last and what questions do PE firms usually ask the references? Will they ask about bullet items on your resume or anything that specific?

4. How should I give my references a heads up if I'm in a group that doesn't openly support PE recruiting? I imagine this is extremely risky especially in the current environment with layoffs and tough job markets, and I don't want to develop a first impression in my group as someone who's trying to leave the job one week after hitting the desk.