Fun, but easy
It was easy, because there was always a lot of time between mice runs. Maybe if you sometimes had them starting one after another, so you had to double click sometimes?
I got a fastest of .1 sec and slowest of .1667, with an average of .13, but I think that is only because there was such a standard time between mice runs. I know it would take a lot more programing, but it would make it more fun and varied.
Also, there is about a second between mice runs, but that gets annoying after a while, even if it was so that slower people would have the same chance. Maybe if you had a timer going from the time the previous mouse was caught rather than from when it left? With a timer going up to a random number. And maybe sometimes you had to get more or less mice, just to vary it up?
Just some thoughts on what could be better, in a sequel.