Moles appear at totally random intervals between a given time frame (the difficulty), that time span decreases as time goes on so the difficulty increases, you may have gotten unlucky and more than three moles appeared the first time : p
There were timers in the development build, I opted for taking them out to give an element of randomness to the game and make the player sometimes feel like "Oh I did it" or "Oh, just missed it" :)
Nevertheless thank you for your feedback, I will definitely take it into consideration! Thank you