Hunter,
Bananas will droop or close up during the day in full hot sun.When you notice it the next day it's probably in the morning or in the evening.Once it cools down at night they open back up and are usually still open wide early in the morning before the hot sun hits the leaves.They close up to conserve water in full sun with high temps.Hope this helps.
Randy

Are you talking about that one rolled up leaf in the center of the plant, because thats the newest leaf and its rolled out because its still growing and it unfurls when it is fully grown. Other than that, many bananas will fold there leaves a little during the heat of the day. I try to give my bananas lots of water to prevent this, but its pretty unavoidable during the heat of the day and it does not damage the plant.
-Alex

Butiaman has it right. Bananas do react to light and sometimes temp. In fact many plants do this. My bananas, during the heat of the day the leaves will almost fold so each side is pointing down (drooping) Then later in the day once it moves into shade or the sun starts to go down the leaves plump back up and become more "normal" looking. They are doing this as a means of keeping cool and not burning. When a leave does this, it is basically are changing the angle at which the sun hits them, helping to conserve water, and avoiding burning / damage. It is quite normal and nothing to worry about. Even well watered bananas will do it. However, it will get more pronounced if a banana has been given less water.

Just like if you keep a banana very well watered, they will "sweat" beads of water off of the edges of the leaves. This water is excess that the plant can not use. Basically, its all about keeping a healthy balance for the plant. Hope that makes sense.

In a pot outside, I would water bananas daily. I usually water my in-ground bananas daily anyway. They LOVE water.