How does a lease transfer work on a GM?

I’ve read some articles and some forum posts, but I have a few questions that hasn’t been answered. I’m interested in taking over a lease on a GM Bolt, about 29 months remaining on a 36 month lease. The transfer fee is roughly $600. I have excellent credit so I’m not worried about that.

I heard that the transfer process takes about a month. It was a one-pay, so I need to cut the guy a cashiers check.

When do I pay him, and when do I take possession of the vehicle?