I'm sure this has been mentioned before but - I realised last night while tearing my hair out trying to complete the Ice Arena [HARD] Special Conditions race that each time I restarted, another day had passed. Even if you quit as soon as the option is available, before the countdown even begins. Simply exit, retry, exit, retry etc etc… as soon as possible. I passed 100 days in a couple of minutes (trying to get to 694 for obvious reasons). I've been playing GT4 since it was released and had never thought about this. I just let the days pass organically until that magic number but this is a short cut.