It's supposed to be 30 days? Then was it changed in FIXT? Because I just did it last night. Started the games, killed the rats, rested until midnight, entered the Vault, did everything there, including the water thief. I think I figured out why I was so confused. After you get the 1000 caps threshold, you can then kill him and it should count for the quest. You're supposed to walk away with a profit of 1800. Once you take the loan and pay back, when he offers 1000, he'll have roughly 2800 (before giving you the 1000) in his inventory. It's been so long, I thought he was supposed to say "I won't loan you more" when it's basically he won't loan you a higher amount. I was wondering about that. Found it really odd he kept walking back and forth like that XD.