I ride as hard as I can, for between 2 and 4 reps. Two is all you really need, so that's all I ever commit to when I start, so I don't hold anything back. If I feel great after 2 I might do one or two more, but I doubt there's much benefit from more than 4 reps.
Two years ago, I started out doing it in 8 minutes in the spring, working down under 7 minutes by late summer. This year, I'm starting out at 6:47. So I'm off to an early start, because I have to be. PBP is only 125 days away. I need to start shifting away from strength and power towards endurance training, but the rando riders finishing ahead of me are stronger than me in the hills. I think I have the materials to accomplish PBP, but there's no point taking any chances.