I recently had the upgrade clear for two passengers going BOS > LAX and LAX > BOS. In both cases, the upgrade cleared automatically somewhere between 28 and 30 hours before the flight. Nothing was needed from me in either case.

I got a different response from an agent re: booking on points. The agent I spoke with said an "all points" booking was not eligible for Move to Mint, but that "some cash" needed to be used for the itinerary to be eligible. It was not clear to me whether the cash paid for taxes on a points booking would count. Rather than risk it, I just booked flights with all cash because I wanted to maximize my chances of using the certificates.