The ten timed challenges trophy is needed to get the plat. It was the last one I got. But I don't know what this bike glitch is. I've heard a few people mention it yet I got the bike trophies first and had no problems. If you think it has glitched then copy your game onto a memory stick, delete the save on your PS3 and start a new game. Do the timed challenges on a clean slate and after you get the trophy copy your original save back onto the PS3.