Creatine can make you spill if your creatine stores are full. If so, the oral creatine is absorbed, but not take up by the muscle cells, leaving it as an osmolite that can draw water in the interstitium (e.g., under the skin).
If you use ith up the the week or several days before a show, your creatine stores will be elevated and the goal of "volumizing" the muscle cells will be accomplished. A 5g creatine dose is cleared from the blood in roughly 5 hours.
You could try to use it with a carb-up during the 24 hr before a show, but the chance of spilling is there. Typical loaing increases creatine store about 20%, meaning that around 30g is take up by the muscle. If you had not creatine (except for that in food) in your diet, you might be safe with, say, at total of 10g of creatine during a 24hr carb-up.
BUT, I think it would be better to have taken creatine during your pre-contest dieting, to hold on to muscle (possibliy), rather that to use to it enhance your carb-up.
Frankly, I use Creatine on weekend CKD carb-ups and haven't noticed any water retention...
-Randy