You basically have 2 laps from when you click play to get the time on before the server gets too bogged down with laps and times. So use the first lap to get the speed on the last sector then your 2nd lap is going to be 'the' lap to get the time. If you fail to better your time then go options>restart>options>quit then go back through the menus to the challenge to make sure the server has completely forgotten those laps. You can still maintain some kind of rhythm with the event and the laps, it's just a more clunky way of going about it. If you do better your time then go round an extra couple of laps, following your ghost for the servers to re-engage the ghosts and then register your correct time. Don't beat your new best ghost before you've got it to stick, otherwise it'll bog down the servers memory of your laps. You'll see if it's worked if you click options and look at the leaderboard while you're in the event.