Once in an online lobby you dont even need to complete a lap, you can keep your game running and YOU WONT get kicked once the race is over achievement pop, look for races that are 3 laps and No qualifying it will go quicker. This can also be done for the remaining online achievements. HOWEVER MANY PEOPLE ARE KEEPING XB ON OVER NIGHT TRY AND JOIN LOBBYS WITH 4+ PEOPLE IN OTHERWISE THE GAME WILL BE ON FOREVER IF NO ONE IS RACING