It says you need that many; but you've got an extra hour. I've read quite frequently that many people have about 4+ hours spare; you've got time to catch up and get that extra 900 kills.
From personal experience, I think it's better to get at least 1.5k kills instead of saving after ever 1k. Running out to the cart and driving up to the SUV takes too long in my opinion, and as the SUV can last for 5k kills (without crashing badly) you don't have to worry about it exploding on you.
If you're still worried about failing, make another save as backup. It's what I'm doing.