There is no minimum, but the difficulty is set to 10,000 which would take a few days for you just to find one share. If your toy supports the --suggest-diff command, set it to 1 and it will happen sooner. I'd prefer if you didn't mine with it except for playing for a short while though; you are not really doing anything useful and are using almost as much of the pool resources as the biggest miners. I won't stop you, but I will discourage you from trying.