I usually work out at night and I was wondering taking creatine, and not drinking tons of water afterwards would be bad. I drink about 1-1.5 gallons per day, but usually after I take the creatine, I only drink maybe another 16 oz, before I go to bed, and I was worried if that was enough. What do you guys think?
You'll be fine. Just make sure you're drinking adequate amounts during the day (and you are).
Your total water intake is more important than trying to time drinking more water after you workout. 16 oz is still enough water after working out. Assuming you are drinking water immediately prior to (at least 8 oz) and during your workout (at least 16 oz). You should be fine.