Yes, the boxes usually gave you 48 hours to reach them. I have been lucky and gotten the key twice and the rewards are decent compared to all the points needed in Soda Squad for something less! There are some levels I have only been able to pass with double fish so I often need more than a few hours!
I have noticed that Batula tends to vary a lot in the time frame given to get the key. I have seen anywhere from about 1-3 hours. When playing hard levels and having to wait for lives to refill the 1 and 2 hour time doesn't seem to be enough. He is good at showing up when I am challeged or about out of lives!